Trapped: the first love By Skyler Sokashima

(A boy named Sky is trapped in his mind forced to be tormented by the monster, Xero of his past that takes the form of black oily mist and a boy-Dasuki who comes and breaks him free only to find out that Sky is the last descendant of the legendary Blue Blood family and heir to the throne of king Belphagor. And must defeat god and the angels before they enslave the humans and take over the world)