The Apocalypse Slayer

Ryuji Leone is the close friend of Rias Gremory, Akeno Himejima, Sona Sitri, and Tsubaki Shinra, or not so secret crush of Akeno and Tsubaki, and the adopted son, and brother of Acnologia, the Black Dragon of the Apocalypse, his brother, Hinata, the Devil of the Apocalypse, his mother, and Graham, the God of the Apocalypse, his father. One day Ryuji informs the girls that he must leave to start his Slayer training, and makes a promise to his four female friends that he'll come back stronger than anything they've ever seen before. Of course, not before revealing to his two fangirls that he knows about their feelings, and will give them his answer once he returns. Years later, and Ryuji returns just in time to help arias win the rating game against her fiancé, Raiser. How will the lives of his friends, and their peerage change now that Ryuji has returned?