Kokuyo

Kokuyo is one of the sons of Satan. He falls in love with Hisui. Together with Hisui, they started living at Shuuichirou's house. He was the first to sense something odd about Shuuichirou, but his attempts to tell that to someone were always getting interrupted, as if some greater force prevented him from saying anything.

[Spoiler] He was prevented by God to speak about Shuuichirou's impending death. [/Spoiler]