When Breaking a Chuubert in Half, the End with the Knob Should Be Better. It's Also Tasty to Drink from There - S3.E50

As the bombing of the Shinsengumi headquarters nears, Hijikata and Okita are still unable to find any means for escape. Only one key exists to unlock the shackles chaining each other. But if the key is used, it will set off a bomb to kill the other. The rule of the devil begins to stir distrust between the two. Though he commends them for not betraying one another, Jigzaw pressures them to make the final decision by displaying a certain item.