One Side of the Soul is the 10th chapter of the Rurouni Kenshin manga.
In Tani Jūsanrō's residence, Kurogasa (a.k.a. Udō Jin-e) kills a few bodyguards and tries to kill his contract's target, Tani. However, he is stopped by Kenshin and Sanosuke, who are the only ones able to resist his Shin no Ippō's power of paralysis.
Saying that he hasn't had this much fun since the Bakumatsu, Jin-e decides that he will fight Kenshin and kill him. Then, as he makes his exit by the same window he came through, he tells his new target to get a real katana and wait for him.