Kokuyo

Son of Satan, The Devil Prince
Kokuyo is one of the sons of Satan and falls in love with Hisui. As stated in Hisuis entry he and Hisui start living at Shuichiros house and watch over Kohaku when she sleeps. Kokuyo is also aware of the first Shuichiros impending death but God stops him from telling anyone else so as to make sure things go as they should.
1