Hisui is one of four Angel Masters of the four natural elements (fire, water, earth, and wind), their 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. They eventually reveal themselves to Kohaku, and also reveal that they have made love with Kokuyo (Prince of Hell) and states that they 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.