The Fallen One - S1.E11

After his brutal defeat, Heisuke drinks Ochimizu and becomes a Rasetsu. An attempted assassination leaves Captain Kondou in critical condition. In order to avenge Kondou, Okita drinks the Ochimizu that Kaoru gave him, also becoming a Rasetsu. Kaoru appears, and reveals that the Ochimizu will not heal his tuberculosis. He also reveals the reason he hates Chizuru. In an ensuing battle, Okita manages to kill Kondou's attackers, but is also heavily wounded by gunfire. With both Okita and Kondou close to death, Hijikata sends them to Osaka Castle to be treated by Doctor Matsumoto.