Hisui

Hisui is one of the four Angel Masters representing the natural elements (fire, water, earth, and wind), with wind being his element.
He is the original reason Kohaku comes to Earth for 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. Shuuichirou offers to let Hisui and Kokuyo stay in his house.

Spoiler