The Black Dragon Emperor that Led the Way

Hikaru Tachibana is a second year at Kuoh Academy known as the Dark Emperor. After being killed by a Fallen Angel, he is brought back to life as Rias Gremory's Devil servant. But, Issei Hyoudou took up her eight pawns. So what piece is he? An experimental one called a Vanguard. As such, he will lead the way to victory for Rias' Peerage. Slightly OP OC OCxHarem