Shukuchi & Soujirou

This page contains content written by Laura Gilkey, also known as Fox in the Stars. She has kindly agreed to my hosting the content previously found on her former domain, shininghalf.com for the benefit of Soujirou fans everywhere. I have made no changes aside from presentation and proper noun spelling for the sake of continuity across this fan shrine.

Soujirou’s Most Amazing Ability

DISCLAIMER: This page was written by an artist (I had a bit of help from my best friend the engineer, but the fact remains). I’m a bit out of my element here, so my calculations come on a “reader beware” basis.

So, you ask…

What is this most amazing ability?

How fast is Shukuchi?

Shukuchi is Seta Soujirou’s most amazing skill, incredible speed that renders him invisible to his opponent. As if that weren’t incredible enough, his powerful legs allow him to reach this speed immediately from a standing start (according to Shishio Makoto, who would know if anyone would). This ability is especially amazing when you realize that the speed at which competitors run the Olympic 100-meter dash is around 22 mph, and they’re not invisible. A cheetah’s top speed is around 60 mph. Cheetahs aren’t invisible.

So, if Soujirou’s Shukuchi is faster than an Olympic sprinter, and faster than a cheetah, how fast is it really? Sanosuke and Yumi didn’t know, but there are some ways we can try to figure out.

Calculating Speed by Footprints

As described in Dinosaurs: The Textbook by Spencer G. Lucas, British researcher MacNeill Alexander devised a method by which a creature’s speed can be determined by studying its tracks (This is in a Dinosaur textbook because the technique was originally intended to recreate Dinosaur speed based on fossil trackways). All you need to know is the length of the creature’s stride and the length of its legs.

So, in Soujirou’s case, we can safely estimate that his legs are about a yard long, or 0.9 meters. His stride can be approximately figured because the room where he fought Kenshin was conveniently floored with tatami mats, and according to a cultural note in my Japanese language textbook, Youkoso! Continuing with Contemporary Japanese by Yasu-Hiko Tohsaku, a standard tatami mat measures about 1 meter x 2 meters. The first time Kenshin sees Soujirou run a few steps short of Shukuchi, there’s a clear shot of the tracks he left. His stride (that is, the distance between the same point on two successive prints–or in this case, craters–of the same foot) crossed about two of these mats shortways, so we can estimate it at around 2 meters.

Now that we know that, we can use the following formula to determine Soujirou’s Relative Stride Length:

Stride Length / Leg Length = Relative Stride Length
2 meters / 0.9 meters = 2.2: Soujirou’s Relative Stride Length

Next, we need to convert Soujirou’s Relative Stride Length to his Dimensionless Speed. It turns out that there’s a linear relationship between these two figures which can be plotted on this chart (scanned from Dinosaurs: The Textbook):

Now, we can convert his Dimensionless Speed into an Actual Speed using the following formula:

Actual Speed = Dimensionless Speed x square root of (Leg Length x Gravitational Acceleration)
and Gravitational Acceleration is 10 meters/second2, so…
Actual Speed = 1.25 x square root of (0.9m x 10 m/sec2)
= 1.25 x square root of (9 m2/sec2)
= 1.25 x 3 m/sec
= 3.75 m/sec

Now, to convert that into a more practical measure…

3.75 m/sec x 60 sec/min x 60 min/hr = 13500 m/hr
13500 meters per hour / 1000 meters per kilometer = 13.5 kph
With some quick conversion, that’s approximately…
8.5 mph
And that is obviously WRONG!

Even if it is a few steps short of Shukuchi, that’s way too slow to be right. Soujirou’s technique must get its speed in some unusual way that this formula doesn’t take into account, I’d say probably the rapidity of the steps—I mean, listen to that; it sounds like a machine gun! Actually, this may very well be a good thing because for this formula to produce a Shukuchi-worthy speed, the Stride Length would have to be impractically long, too long for him to have the kind of control over his travel that he obviously does.

So, if we can’t get an accurate estimate of Shukuchi’s speed that way, how can we figure it out?

The Speed of Invisibility

Of course our biggest clue to the speed of Shukuchi is the fact that it does make Soujirou invisible to his opponent. So, how fast would he have to be going to become invisible? It’s a lot more than 8.5 mph, I’ll tell you that right now.

Neither of us has any expertise in human optics, but my wonderful demigoddess-of-a-best-friend Kati hypothesized that in order to be completely invisible, Soujirou would have to enter and leave someone’s field of vision (which would vary by distance, but we’ll estimate it at about 30 feet) in the time it takes for the human eye to register the stimulus, which we think is about a tenth of a second.

So, if these guesses are right, then he would have to travel 30 feet in 0.1 seconds, and the math for this one is much easier…

(30 ft / 0.1 sec) x 1 = (30 ft / 0.1 sec) x (10/10) = 300 ft/sec
300 ft/sec x 60 sec/min = 18000 ft/min
18000 ft/min x 60 min/hr = 1,080,000 ft/hr
(This is starting to sound pretty darn fast, isn’t it?)
1,080,000 ft/hour / 5280 ft/mile = 204.5…
So, given the approximate nature of these calculations, we can say that Soujirou is traveling at about…
*200 mph* (320 kph)

That’s over three times as fast as a cheetah at top speed, and about nine times as fast as an Olympic sprinter. I’m not even sure that a normal person’s body could withstand the stress of that kind of speed, and certainly not such immediate acceleration to it. Keep in mind, too, that this is only a calculation of the minimum speed that would make him invisible; true Shukuchi speed is likely even faster!

Hideo Tsuneoka on Speed and Vision

This theory was sent to me by Hideo Tsuneoka.

Soujirou… Invisible… Great episode…

Anywho… I would like to say something… The human eye registers moverment in an odd way… Soujirou wouldn’t be truly invisible, I do not think… You know how when a car is going from stopped, to driving? Notice how the hub caps go the proper way at first, than it seems as if the wheels themselves are turning not forwards, but all of a sudden backwards??? This is because the speed at which they move is faster than the human eye can register, so we are seeing it backwards, as we only register things slowly compared to how fast it is moving… Let’s say it was a line of sticks, moving in a straight line…

<<< | | | | | | | <<<

They are going left… But, if they were going too fast, we would see them as eventually going right… They go too fast for our eyes to register…. So we are seeing it like this… The brackets indicate what we see…. Let’s say the first bar is what we are looking at… If it is moving fast enough, we will see it as it nears the place of the stick that is before it. And, thus, every stick, we see it in place of the one before it…

<<< (|) | | | | | | <<< What we are trying to see
<<< | (|) | | | | | | <<< What we actually see.

So, if you keep going, it would appear to be going backwards, rather than forward…

So, let’s say Soujirou is moving so fast that our eyes cannot register where he is at all times… This does not make him truely invisible. We would see Soujirou in random places, around the room, flickering, as if a hologram was in various places…

Well… That is my theory anyways… That’s actually a fabled Ninjutsu technique as well… :-)

Thanks, Hideo! That makes a lot of sense, and it would’ve looked really cool, but I guess Aoshi already spent that nickel…

Actually, though (adding this paragraph long after the fact, but it seemed most appropriate here), I have noticed something in a recent re-watch that seems to display this effect. In episode 54, when Soujirou first demonstrates his Most Amazing Ability by running three steps short of Shukuchi, he disappears, but of course we see those bursts from his footfalls. At that point, they follow a pretty coherent path. However, at the end of 55/beginning of 56, when he’s increased his speed to one step short of Shukuchi, we still see them, but at that speed, the bursts seem not to follow a path, but to occur at random points, a distinction also noticeable in the manga.

A Drop of Water

This theory is based on an e-mail sent to me by Sonny Lo, although I did all the number-crunching. Sonny writes:

In the episode, you would have noticed that Seta made his attack in the time it takes a drop of sweat to drip from Sanosuke’s face (Well, actually, it was Yumi’s face ~L.) to the floor and with time to spare. Taking that into consideration, the true speed can be calculated by dividing the distance moved (the number of tatami mats covered) by the time taken for a drop of water to fall to the ground. I would give an estimate on the distance traveled though.

That is a very good idea which I had previously neglected, but, with thanks to Sonny, I have now corrected that oversight. Thankfully I was able to consult with my best friend Kati for the math on this one.

I don’t know the entire acceleration equation, but Kati boiled it down for me so that the time it would take that drop of sweat to hit the floor could be figured thusly:

time = square root of ([height x 2]/acceleration)

According to Kati, Acceleration = [32.2 ft/sec2]. The official character stats I’ve found give Yumi’s height as 5’4″, but since it isn’t falling from the very top of her head, I’ll round it off and say that drop fell 5 feet. This gives us:

time = square root of ([5 ft x 2]/[32.2 ft/sec2])
= square root of (10 ft/[32 ft/sec2])
= square root of ([10 ft/1]x[1 sec2/32.2 ft])
= square root of (10 sec2/32.2)
= square root of (0.31 sec2)
= 0.56 seconds

Next we estimate the distance traveled in that amount of time. I went through the footage carefully to get these estimates. Before the strike, there was a nice shot of Soujirou and Kenshin from the side, and using Soujirou’s height as a basic measure*, I estimated that they were standing about 20 feet apart. In the attack they made while the drop was falling, they passed each other, and figuring out how far apart they ended up was a little bit trickier. However, after this attack, neither of them had moved when Soujirou started his just-short-of-Shukuchi attack, which can be measured against the Tatami Mats on the floor. (See above: tatami mats are about 1 meter x 2 meters.). The first shot of Soujirou’s explosive footsteps I am disregarding–the distance it would yield is completely implausible, so I can only assume that this was sort of an establishing shot to give us viewers a feel for the ability and took place outside the linear progression of the scene (this is the reason why I don’t use distance-per-second-of-tape to measure the speed–artistic liberties were obviously taken there). After that, there is a view over Kenshin’s shoulder of Soujirou running toward him, and I take the first visible footstep in that shot to estimate the distance—it was 9 tatami mats shortways from Kenshin, and I will round 9 meters to approximately 30 feet (it’s actually 29.53 feet, but this is all necessarily general anyway). So, I feel safe in estimating that each of them closed half the distance between them when they started, then covered half the distance between them when they finished, so:

(half of 20 ft)+(half of 30 ft)
=10 ft + 15 ft
= 25 ft

So, if they each moved 25 feet in the time it took that drop of water to hit the floor:

25 ft/0.56 sec = 44.64 ft/sec
x 60 sec/min = 2678.4 ft/min
x 60 min/hr = 160,704 ft/hr
/ 5280 ft/mile =
30.44 mph (48.98 kph)

Okay, so maybe after saying 200 mph, this doesn’t sound so great, but this figure is actually pretty impressive, for several reasons:

  1. See above: that’s significantly faster than an Olympic sprinter.
  2. How many things do you know of that can accelerate to 30 mph in half a second?
  3. This was before Soujirou even started doing the Shukuchi thing.
  4. That drop of water was actually halfway to the ground when they started running!

Watch that sequence closely. It’s true. So yes, I took you through all of that for an erroneous figure and I’m sorry, but I thought it might be nice to do to get some perspective and whatnot.

So, how fast are they really going? Well, we simply calculate the time it took the drop to fall half the distance:

time = square root of ([2.5 ft x 2]/[32.2 ft/sec2])
= square root of (5 ft/[32 ft/sec2])
= square root of ([5 ft/1]x[1 sec2/32.2 ft])
= square root of (5 sec2/32.2)
= square root of (0.16 sec2)
= 0.4 seconds

Now, we subtract that from the time it took for the entire fall:

0.56 seconds – 0.4 seconds = 0.16 seconds

So…

25 ft/0.16 sec = 156.25 ft/sec
x 60 sec/min = 9375 ft/min
x 60 min/hr = 562,500 ft/hr
/ 5280 ft/mile =
106.53 mph (171.41 kph)

And, as I said above, this was before Soujirou even started showing his “Most Amazing Ability”!!! That 200 mph estimate continues to hold water!

Er, no pun intended.

The Meaning of the Word

Enemyjr@aol.com sent me this opinion:

the ability shuku chi also has a meaning in korean and both meanings dont apply to speed, but they instead apply to shortening the distance between two points. like bending the ground.. get it?

Now that you mention it, I do remember at some point seeing “Shukuchi” translated (on The Soujirou Shrine, although I can’t seem to find it there now) as “Reduced Earth,” but I had never thought of it that way before.

However, I personally find this idea a bit hard to buy for a few reasons: First, I can’t see it, and yes I know that that would be the point, but from the “academic” standpoint of getting to the bottom of this, I have to work with what I can see and measure. Also, just short of Shukuchi, we did see his footprints along his path, so he obviously did cover all that distance. The more important reservation I have about this is that while I admit that Rurouni Kenshin employs its share of fantasy physics, it does have some limits, and I’ve seen both the TV episodes and the manga go out of their way to debunk things that got too supernatural in their seeming. The ability to run 200+ mph seems more in keeping with the laws of the RK “universe” than the ability to warp space.

However, that’s just my opinion. And disagreement aside, I do really appreciate the input! Also, see below under Literarily Translated for some interesting background on the term.

Speaking of Fantasy Physics

These calculations were done for me by my Soul-Sister, Kati, who is also a professional engineer.

Now that I’ve characterized this kind of running speed as “more plausible” in my opinion than something else, let’s get some sense of just how implausible it really is.

Here are Kati’s calculations of the force that Soujirou would have to exert with each footfall in order to achieve the final speed for the “Drop of Water” estimate (see those figures for the starting points of these calculations). Keep in mind this is before he even started using Shukuchi, and Kenshin can achieve this speed, too.

Force = mass x acceleration
which approximately equals: mass x [(change in velocity) / (change in time)]
= 51kg (Soujirou’s weight) x [(156.25 ft/sec - 0) / 0.16 sec]
= 15,180 Newtons
= 3,413 lbs.
But we’re not done yet!

This is just the force forward that Soujirou needs to achieve that speed. He also needs to exert force downward to generate enough friction against the floor to propel himself forward rather than his feet slipping and him running in place.

Friction = µ x N,
where µ = coefficient of friction and N = normal force (the force straight down, which is what we want)

According to the law of equal and opposite reactions, the friction will be equal to the force moving forward (calculated above), and a typical tile floor, assuming Seta-san is not slipping, has µ of 0.5 to 0.7. For the sake of her own sanity, Kati used 0.7 to approximate the tatami mats. So…

N = force moving forward / µ
= 15,180 Newtons / 0.7
= 21, 686 Newtons
or 4,875 lbs.
Scared yet?

Now we combine the force down and the force forward like the legs of a right triangle to find the “hypoteneuse”, which will equal the total force Soujirou’s leg is exerting with each step. (Force is a vector, Kati explains, but what I’m passing on to you is the explanation of that explanation that she needed for my non-mathematical self.)

a2 + b2 = c2
(15,180 Newtons)2 + (21,686 Newtons)2 = Force2
= 26,471 Newtons
or 5,950 lbs
That’s almost 3 tons!!!

As for what this actually means to the human body, she’s approximated the cross-sectional area of the weight-bearing bones in Sou-chan’s legs as a circle with a 1.5″ diameter and calculated the pressure being applied…

Area = π x radius2 = (π x diameter2)/4
= [π x (1.5in)2]/4
= 1.767in2
= 1.14 x 10-3m2

Stress = Force/Area
= 26,471 Newtons / 1.14 x 10-3m2
= 23.2 MegaPascals
= 3,367.8 psi
(that’s over one and a half tons per square inch)
-or- Atmospheric Pressure x 229

To put that last bit in perspective, Atmospheric pressure is about 14.7 psi. A car tire (four of which lift a car off the ground, if I may point out the obvious for the sake of my point) is usually inflated to 30 psi.

Could human bones withstand this amount of force? I don’t know. At the very least, the engineer says, having this kind of stress applied to the bone in such a repetetive manner would have caused fatigue failure by now in any normal person. Worse yet, it’s not just bones that have to deal with it; there are also all the softer connective tissues that have to keep his knees and ankles in one piece under such pressure.

And there are a variety of other factors Kati stopped short of calculating which would further compound the impossibility of this feat…

Of course, physics says bees can’t fly, too. But suffice to say, Soujirou’s Most Amazing Ability is a truly amazing ability!!!

And we have to respect those Waraji laces for hanging in there as long as they did!

Point of View

Here’s a view from Robert Leland:

I have to ask you that.. You do know it’s an anime? It’s drawn and fictional… Whatever happens in the anime won’t in any way relate to the mechanics of the real world.. so a phyiscs explanation of the speed is completely illogical.

Yes, I know that, but maintaining this page has been so much fun! ^_~

But if you want to compare it to the real world you can fail all the theories on the page by taking into the account the speed of an airplane (around 500mph?) or a spaceshuttle (dunno the speed of this.. but it’s faster than a bullet).. And consider that neither of these two are invisible, so anything lower than that wouldn’t be invisible either.

Now I just realized something… Which I guess has something to do with preception… But a bullet is pretty much invisible, a space shuttle isn’t.. So I guess it follows that how quickly it turns invisible depends on the size of the object and the distance away from you it is… If it was able to travel through your field of vision in less time than it takes your eyes to register it it would be invisible, so the further away it was the quicker it would have to travel (your hand is close to invisible if you move it past your eyes real quickly, close to your eyes)

That is very true, and as compared to a space shuttle or an airplane, a human body in the same room with you would be relatively small and close.

A related realization is how this is effected by the way your eyes track an object. Only a theoretical point of view is fixed, after all. For example, if you’re riding in a car, watching trees go by outside the window, if you look at one tree as it comes up and watch it until it disappears from view, you’ll see it clearly, but if you look out the window in a “fixed” way, you’ll see streaks—that is, the objects become more invisible. Perhaps Soujirou’s Shukuchi technique uses not only sheer speed, but also changes in direction or some pattern of movement to throw off someone trying to track his path with their eyes. It’s possible.

Speed of Light, Speed of Mind

These are a couple of thoughts from Jimmy Lee:

1) What we see in a person is the reflection of light on various levels (Violet, Ultraviolet, etc). So in order to escape the reflection of light, you would have to exceed the speed of light. Which according to our pal Einstein, is impossible as a person would disintegrate into non-existance, then again, this is anime. Given this particular theory, Soujirou would be traveling at least 299,792,458 meters/sec. There’s your physics explanation. Even if he were to go over 200 miles per hour in front of you, you would still see a blur of his path, because his body is still reflecting the light back to our eyes

No question, he surely would be invisible if he were travelling at or over the speed of light, and although I’m no scientist, I’d say it would be true that he would have to go that fast to avoid reflecting the light that vision is a perception of and thus be absolutely invisible. However, I do think there is a lesser point at which he would be essentially invisible. To base an example on the above view (Point of View), if someone standing fairly close to you fired a gun across your field of vision (and assuming you didn’t blink), the bullet would travel far below the speed of light, but it would still be so fast that you couldn’t really see it. Perhaps if measured technically, there would be a blur in its path, but at some point it becomes such a faint blur that the mind no longer picks it up. We just don’t register every single reflection of light that enters our eyes, every single moment. If we did, then subliminal messages would never have worked or been secret.

Besides (and speaking of “the speed of” one thing and another), it occurs to me that we can probably assume an upper limit of about 700 mph here, because at that point, depending on atmospheric conditions, Sou-chan would risk overtaking the speed of sound and creating a sonic boom.

2) Real world kendo masters have been known to not really move that fast, but simply appear to be moving that fast through optical illusions. If a person were to accelerate at a constant rate and not shift their upper body, in the perception of your opponent, you would look like you just stood their and reappeared in front of your opponent. There is a psychological explanation for all this, but I really have no desire to get into it

I don’t have the psychological explanation for this either, but I can definitely see where it would be so. This example doesn’t strictly apply to Soujirou’s apparent invisibility, but it brings up the point that a technique like Shukuchi wouldn’t necessarily rely on sheer speed alone, but also on moving in a way that the human eye and the human mind wouldn’t expect and thus couldn’t follow.

The Fourth Dimension

Michelle e-mailed me to elaborate on Enemyjr’s point above, under “The Meaning of the Word” (the suggestion that Shukuchi might involve essentially warping space).

Sounds ridiculous, but is actually quite probable in a higher dimension, ie. the 4th spatial dimension. (Oh no! RK’s turning into a sci-fi series!) It’s kind of far out, so please bear with me …

Let’s say Soujirou wants to get from one point to another using Shukuchi. Visualise the line between Soujirou’s initial postion and his final postion and imagine that *only* this line can be seen with the human eye, as surely as we can only see 3 dimensions in reality. This line runs along one dimension.

Now, bend the ground. Your line becomes a curve. Curves are one dimensional in and of themselves since any point on the curve can be described by a single coordinate. However, the orientation of the curve relative to the original line means the whole bending process actually existed on a two dimensional plane. So, bending the ground in this (1-dimensional) manner requires the involvement of a higher dimension than previously did not exist.

(Kati-chan wants me to throw in a correction at this point that a curved line is two-dimensional because it would require two coordinate axes to describe—remember the X/Y graphs you had to do in high school? A straight line could just be lined up on the X axis, and then any point on the line could be described using only a value for X—one coordinate, therefore one dimension. But if the line curved, some of the points would come away from the X axis, and you would need a value for Y (i.e., a second dimension) to describe them. However, I get what Michelle is saying here; stay tuned for a layman’s explanation. )

Apply this concept to 3D space. It is thus possible for the ground to fold imperceptibly to the human eye, because this folding *occured in the 4th dimension*.

Lest this dimension talk sound all Twilight Zone-ish, there is some quantum physics theory that only works in the 10th and 26th dimensions, called the Superstring theory. It’s way over my head so don’t ask me how it works. ;^_^

But yeah, even so I admit this is a little far-fetched … just something I thought might be possible. If you’re interested in this stuff you could read A Wrinkle in Time by Madeleine L’Engle. It’s a fantasy children’s book which uses this concept of travel. L’Engle seems to think it involves a “tesseract”, which is a name for a 4-dimensional hypercube. (See http://www.geom.umn.edu/docs/outreach/4-cube/ for a couple of animations on the subject.) But other than using higher dimensions, I have no idea what she’s on about!

Ack. Hope this goes some way towards unveiling the mysteries of the Shukuchi. Dratted Japanese. If they invented the art of manipulating higher dimensions by the 19th century, no wonder Sony came up with the walkman! *grin*

I have to admit, not being physics-minded, my initial reaction to this one was a good hearty “Eh? Eh?? Areh?” But thankfully we have Kati-chan to field the more technical questions, so I’m mostly paraphrasing her responses here. In fact, she apparently read this into Enemyjr’s suggestion (which I did not). Her short answer: “The tesseract was considered, but we’re limiting the question to Newtonian rather than Relativistic physics.”

In her long answer, she explained a tesseract pretty much how it was explained in A Wrinkle in Time, which I was able to understand better (I have read A Wrinkle, but it’s been at least ten years). Say an ant wanted to walk from a point on one end of a sheet of paper to another point on the other end of the sheet. If this ant had a human accomplice, they could simply fold the sheet so that the two points met, making the ant’s job easy. In order to do this, the paper—effectively two-dimensional when it was laying flat—was folded into a three-dimensional form. The theory Michelle is talking about is that three dimensional space could, in a similar manner, be folded into a four-dimensional form to bypass part of the path between two points.

However, I think what I said regarding Enemyjr’s view, about what is and isn’t possible in the RK universe, includes it seeming that the series takes place in no-more-than-three dimensional space. Personally, I do feel that this is straying a bit too far into the realm of science fiction, but feel free to disagree! After all, the balance of fantasy and reality in RK is an unusual one.

I Love My Brother

Yes, that’s right, my brother. To my knowledge, he’s never even seen RK, let alone episode 54, but he was browsing my site, and having been a math major in college, became interested in this whole Speed of Invisibility question, and sent me several e-mails with his views, which I’m arranging here as best I can…

I think you’re quite correct in rejecting any of the warped-space types of theories… The ability to warp space would indeed make him able to move fast, but I don’t really think it’d help him become invisible. It’s all in the relativity. If, relative to Soujirou, the universe were to become distorted, then it would logically follow that relative to the universe, Soujirou would be distorted. If he were actually “warping” space so that the distance was shorter relative to him, then relative to the viewer, the distance would stay the same and he would “stretch out” and appear distorted, sort of like the Enterprise in the opening credits for “Star Trek: The Next Generation.” Obviously, stretching yourself out bigger would not be the best way to become invisible. ;)

Anyway, I just thought I’d mention that Soujirou’s choice of dark clothing has a dramatic effect on how fast (or “slow”) he has to go to become imperceptible. The human eye registers a “flash” of light much more readily than it registers a brief interruption of light. Thus, by dressing himself to be a darker color than his surroundings, he effectively makes Shukuchi speed much easier for himself.

Here’s an experiment you can try: Find a pen, pencil or other similar small narrow object that is white in color and another one that is black or some dark color. Swipe each one in front of your eyes once quickly. (Look away from the computer screen first; staring into a light source will affect this experiment.) Which one did you percieve more readily? The flash of white should have been much more perceptible than the flash of “darkness”.

Or think about this: Which would attract your attention faster, the lights in the room flickering for a split second, or a camera flash?

I actually did try the suggested experiment sitting here at my desk with a white inkpen and two mechanical pencils, a charcoal-gray one and a blue one. Admittedly not a tightly controlled test, but with the white pen I did see a white swath that was much more noticeable than what I saw with either of the pencils.

It also occurs to me that Soujirou might be taking advantage of this not only in his choice of clothing, but also in his choice of battleground. As my brother says, looking into a light source will affect the experiment in that even a light-colored object becomes an “interruption of light” if it’s getting between you and a light source and thus casting its shadow on your eye. The many translucent (I’m assuming paper) windows of Mugen no Ma admit diffuse but intense sunlight, giving these episodes their characteristic “glow” and effectively making the whole area of the windows a light source. Thus, by running in front of them, Soujirou could take advantage of the backlighting effect.

Brother went on to say…

You may have noticed my choice of the word “imperceptible” rather than “invisible”; I did that on purpose. Being “imperceptible” is much easier than being “invisible”, and “imperceptible” is really all that Soujirou has to achieve.

Thinking specifically of chasing a housefly or other sort of flying insect: Even in flight, a fly is obviously not invisible. If you can focus on it, you can see it. However, as a self-defense technique, a fly can become practically *imperceptible* using a combination of its small size, its dark color, and quick, erratic movements. Once you lose track of it, which you will do when it changes direction, it’s very difficult to find it again. Imagine if it were going twice or three times as fast; you probably wouldn’t even have those brief flashes of “hey, there it was, darn, where’d it go” that you get while fly-hunting.

I was thinking about the “human optics” factor involved, and I found this site:

http://www.100fps.com/how_many_frames_can_humans_see.htm

It’s actually talking about flicker-free refresh rates and that type of thing, but it says clearly that an interruption of light must be faster than 1/100th of a second to be imperceptible (“flicker-free”), whereas a flash of light must be faster than 1/500th of a second.

So, Soujirou’s body, since he is dressed in dark clothing and is therefore an “interruption in light”, must completely enter and leave a specific point in the viewer’s field of vision (not the entire field of vision, just one point) within 1/100th of a second. If we assume that he is two feet wide, then this means he must move at least two feet (perpendicular to the viewer) in 1/100th of a second. That’s 200 feet per second, or (doing math) 136.36 mph. Since not all of his movement will be perpendicular to the viewer, the 200 mph is sounding about right for a minimum. (This is also assuming that the field of vision itself is not moving relative to Soujirou, but with his amazing reaction times he could make correcting motions to make up for any eye movement…)

Obviously, the size of the object (Soujirou) is a big factor; if he were twice as wide, he’d have to move twice as fast. Which is why planes moving 200 mph are not, in fact, invisible; they’re too big to perform Shukuchi :)

Then again, of course, we could go with Terry Pratchett’s explanation [in his Discworld novels] of why Death is invisible, by saying that the subconscious is quick to discard nonsensical sensory input. “Hey, that looked like a guy running around at 200mph! Naah, that’s ridiculous, there’s nothing like that over there…”

While I daresay Kenshin and co. have seen enough of this kind of thing to overcome that last hurdle (especially since Kenshin can come close to that speed himself, and could put a name to Shukuchi when he saw it), I’m sure Soujirou generally does enjoy a substantial “never knew what hit them” factor.

As for the rest, thank you thank you thank you!! A viewpoint with actual numbers in it! Math I didn’t have to do myself! ^___^

The original Speed of Invisibility estimate was admittedly a sloppy one; it rather amazes me how many tests the 200mph estimate has held up to.

Unless of course your money says that Sou-chan could still do this dressed in white against a dark background. Then we’re talking about more like… ::does some quick math:: 700 mph. 0_0 Whoa, straying into Sonic Boom territory there…

Brother later did make one last observation based on the relativity issue: If Shukuchi speed makes Soujirou invisible to others, it would also logically follow that it would make them invisible to him, since relative to his viewpoint, his surroundings are moving at Shukuchi speed. Since his movements aren’t unpredictable to himself, I’m sure he could keep his eyes trained on his target and avoid this effect, but anything he wasn’t specifically tracking, he wouldn’t be able to see. ::gets a mental image of Sano unexpectedly charging in and Soujirou wrecking into him at 200 mph… Itai no da…::

Literally Translated

Genie-chan e-mailed me with some fascinating further information on The Meaning of the Word…

Being a Korean myself, I know the term as well. This term appears in ancient fantasy novels, most noticeably in the ancient Chinese novel of the stone monkey. I forget the title, or at least am unable to provide one in Chinese or Japanese. I apologize. Anyway, the protagonist of this novel, the stone monkey, uses Shukuchi. As you probably know, Shukuchi merely consists of two (originally Chinese) characters that mean “reduce” and “earth” respectively. Supposedly, the user is able to travel very fast by “folding” earth. Or something like that. Basically, someone who can do “magic” can travel very fast using Shukuchi method by magically reducing the distance.

However, Soujirou’s Shukuchi isn’t called Shukuchi as a literal reference. According to Shishio, the technique is called Shukuchi because it’s so fast that it looks as if the user cast some spell to magically reduce distance (“fold earth,” so to say) between himself and the destination/target. It is a reference to the old “magical” ability (or spell), but it does not necessarily mean that Soujirou is using that very method. In my opinion, it’s more likely that people called the technique “Shukuchi” because the name fit.

I’ve also read a bit in Suikoden (another ancient Chinese novel) where some of the characters used travelling magic, although I don’t know whether it was Shukuchi or not. I hadn’t known about the connection with older literature, and found this really interesting. Thanks, Genie!

And The Vast Unexplored…

Sonny Lo had one other thing to say:

Taking in to consideration the speed of the Hitten-mitsuguri technique Kenshin uses, which it’s speed can be calculated in another way, he is able to block or lessen the blow of the Shukuchi. So the speed would be a bit faster or almost the same as that of the hitten-mitsuguri ryuu.

That’s what I think anyways…

That is true. Shukuchi is slightly faster than Kenshin’s Hiten-Mitsurugi-Ryuu. However, that’s getting beyond the scope of this page. Besides, I’m not a math person, and Soujirou is the only one I love enough to crunch numbers for…

Is this the Final Word?

That’s sort of up to you. As you can see, much of this page is made up of submissions from others, but by now it’s reached the point where everything major seems to have been said, so I’ve stopped accepting submissions for this page. But don’t let that stop you from using this as the jumping-off point for your own “How fast is Shukuchi?” quest!

Everyone who’s written in has my thanks, and here’s to the question!