Hisui is one of four Angel Masters of the four natural elements (fire, water, earth, and wind), his element being wind. Hisui is the original reason Kohaku comes to Earth the first time, as the Angel Master disappeared during a meeting at the bridge between Heaven and Hell. He eventually reveals himself to Kohaku, and also reveals that he has made love with Kokuyo (Prince of Hell) and states that he and Kokuyo cannot return to Heaven or Hell because of it. Shuichiro offers to let Hisui and Kokuyo stay in his house, and this is where they stay for the next 100 years after pledging to look after the sleeping Kohaku.