Kokuyo is one of the sons of Satan, and falls in love with Hisui. As stated in Hisui's entry, he and Hisui start living at Shuichiro's house, and watch over Kohaku when she sleeps. Kokuyo is also aware of the first Shuichiro's impending death, but God stops him from telling anyone else so as to make sure things go as they should.