闇染Liberator －闇堕ち勇者と堕ちる戦姫－

Haruomi was a hero sent to another world to kill the demon lord and when he did, he wished to going back to Earth along with the Goddess Ninia, however she denied to go with him and decided to just sent him back to Earth alone. He was, once again, in earth attending a very prestigious school he is a part of the student council which he wish to turn into his harem. 

After trying to save a friend of his, Haruoumi find he has the demon lord's soul he killed within him, not only that but the goddess knew that the demon lord's soul went to earth so she selected a few girls that have been previously sent to another worlds to fight demons lord and gave them once again power in order to kill him and destroying the demon lord's soul. Now he has no choice but cooperate with the demon, so he'll try corrupt the heroes and get their magical power in order to save himself, get his long wished harem and be free of the demon lord soul.