Kasshin-ryū Reborn is the fourth chapter of the Rurouni Kenshin manga.
On the second day of Yahiko's training, while Kenshin is absent from the dōjō to buy food, and as Kaoru is about to start teaching Yahiko, former students of Kaoru burst into the dōjō asking for help. They are soon followed by a gang of outlaws, the Hishimanji Gurentai, who start attacking the dōjō with a cannon.
As Kaoru soon learns, those former students of hers got drunk and attacked the Hishimanji with their swords. As their former teacher, Kaoru feels responsible for their dishonor and steps outside the dōjō to meet the gang of outlaws, stating that she will take all the blame. This prompts Yashiko to follow her and attack the Hishimanji's leader. The latter then states that he will kill Yahiko, but before he can attempt anything, Kenshin comes back from shopping, telling the outlaws to stop their actions.
The Hishimanji's leader, despite one of his men advising him otherwise, orders the firing of the cannon at Kenshin, who cuts its ball of clay in half with the edged part of his katana, to the shock of those present. The outlaws then go away, leaving the dōjō alone.
Kaoru's former students also go away, in shame, being told by Kenshin to forget they were ever students at the Kamiya dōjō and to never again pick up a sword. The rurouni then consoles Kaoru, telling her that while she can teach people, she won't reach all of them. Yahiko then tells Kaoru to stop crying, that it isn't like her, and, determined to become as strong as Kenshin, tells her that he'll settle for her as a kenjutsu instructor.