Hisui is a main supporting character in the visual novel and anime series Tsukihime. She serves as one of the twin maids of the Tohno household, alongside her sister Kohaku. Hisui is known for her quiet, reserved personality and unwavering dedication to Shiki Tohno, the protagonist. Despite her emotionless demeanor, she is deeply caring and plays a significant role in the emotional development of the story, as well as its various branching routes.