Zip Up Your Fly Nice And Slowly (S01E148)

During their routine night patrol Hijikata and Okita are attacked and kidnapped by an unknown assailant. When they wake up, the two find themselves chained together and imprisoned inside an abandoned room. As the two come to realize how bad the situation is, a creepy man speaks to them over the monitor. The man, who calls himself Jigzaw, reveals that he has placed a bomb at the Shinsengumi headquarters, and that the only way Hijikata and Okita can escape is for one to kill the other! (Crunchyroll)