Leon's best friend, a childish sidekick who often engages in wacky theatrics and carries his head around whenever it gets cut off.

Spoiler

Their real identity is an AI, being one of many living within Planet's code as a result of Shiro/Kojirou attempting to bring back his dead daughter. However, Sasumata is the only one aware of their true nature as such, which makes them question the nature of their existence and purpose in life constantly.