Koji Kashin(Jpn. - 果心居士 - "Kashin Koji") is an elderly doctor within the "core" Itto-Ryu.
Kashin is introduced as one of the core Itto-Ryu, along with Dōa and the others, but is not seen again until later when Dōa commonly comes to visit him in his medicine shop.
When Rin brings Dōa with her to find Manji and Isaku, Kashin gives Ozuhan a map of the Edo Palace to bring to the two, in order to help them find the others. Later, the gate to Edo Palace is opened by the guards after a load of innocent men, turned criminals in order to be experimented on, come rushing to it. Kashin, Anotsu, and a few fellow Itto-Ryu members are seen ontop a hill watching from the distance.
When Koji and the Itto-Ryu are leaving Edo he splits off from the pack and is followed by Inroku Ban, Ryo Soma, and four other Hebigumi. The rest of the Itto-Ryu soon come back to Koji, but the six Rokki-dan in pursuit keep chase into a mountain. Six of the new Itto-Ryu recruits are killed by Ryo supported by Ban, but when the two split up to find the Hebigumi they were with, Koji's pots filled with Seashells, and Nitric acid used to release carbon dioxide knock Inroku down. Koji explains the nature of the pots, and that the traps set up were just to get the Rokki-dan exhausted so they breathe more heavily and take in more carbon dioxide and eventually die. Koji says that Ban is a special case because he can take out his enemies easily without moving because he is a sharpshooter, but directly breathing in the Pot's exhaust was his downfall. Koji takes out acupuncture needles and offers a painless death to Ban, but Ban shoots himself in the leg in order to regain consciousness and proceeds to shoot Koji in the heart. Koji kills Ban by throwing his needles straight into his head and reveals that the blow to his heart was softened by other needles he was carrying. Koji then encounters Ryo who appears to be unconscious from the carbon Dioxide, and he contemplates what to do in order to warn the Rokki-dan of the remaining Itto-ryu's power. He throws a needle into Ryo's shoulder and picks up her face, wondering why a young woman like her is being dragged into a samurai's work. three arrows hit Koji in the back, and Ryo stabs him in the throat with a fourth. Koji pulls back, and tries to throw his needles at her, but falls to the ground, and dies.
Weapons and Abilities
Koji's main weapons are Pots filled with Seashells and Nitric acid, which release carbon dioxide, and slow down the opponents breathing, eventually knocking them unconscious. Apart from that Koji carries around a set of acupuncture needles, which he mostly uses in pairs of four. He also carries around a small tanto which he never actually made any use out of, as he was killed while trying.
Koji is most likely one of the weakest, and least agile of the Itto-Ryu in terms of combat strength, but if he's given a chance to prepare for a battle, he claims he would be able to take down all of the Rokki-dan alone.
Dōa and Koji are shown to have a somewhat friendly relationship, and she visits him often in his shop, but he is always angered by the fact that she calls him his real name when he is trying to cover up for himself.
Sosuke is shown to have trusted Koji to act as a decoy against the Rokki-dan and knew that he was more capable than anyone else, as he would have the territorial advantage.