Yubikiri

is a technique of Shunsui Kyōraku's Shikai, Katen Kyōkotsu.

Description
When using this technique, both Shunsui and his current opponent become forced to tell the truth. If either of them lied to each other, after the first lie, the liar’s fingers would become numb. After the second lie, all the bones in the liar’s body would become incapacitated as though a fist had crushed them, and at the third lie, the liar would be assaulted with excruciating pain. Shunsui does note that Katen is not fond of him playing this game with another person, hence why he can only rarely use it. The game this technique represents is the pinky swear.