Weapons & Soujirou
During the Kyoto Arc, Soujiro uses four weapons. The first two are ordinary weapons: a wakizashi given to him by Shishio the night that his family was about to kill him and a small blade used to assassinate Okubo Toshimichi (most likely a tanto).
The last two are famous blades based on actual weapons.
Nagasone Kotetsu
The Nagasone Kotetsu actually belonged to Shishio. However, when Senkaku was defeated by Kenshin, Shishio lent the blade to Soujirou and asked him to show them his tenken.
During the battoujutsu face-off of Soujirou and Kenshin, the blade was damaged beyond repair and Kenshin’s sakabatou was cut in half.
[...] Kotetsu is one of the 31 greatest smiths. Any swordsman would kill to possess it if he could. [Yumi, ch71]
In reality, Nagasone Kotetsu is the name of a famous Japanese swordmaker during the Edo period and there are claims (however disputed) that he created only 31 swords bearing his name.
Kiku Ichimonji Norimune
The Kiku Ichimonji Norimune which he used against Kenshin in their final battle. It is implied that it belongs to Soujirou. At the very beginning of the battle, it is given a small crack by Kenshin’s new sakabatou.
Kiku Ichimonji… A sword so exquisite, rarer than the Nagasone Kotetsu… has been cracked?! [Yumi, ch128]
In reality, the Kiku-ichimonji is a collective name for swords created by 13 smiths to the Emperor Go-Toba in 1208. One sword was created each month for a year (with one intercalary month between the 5th and 6th months). The Norimune blade was created in the first month.