Regressor's Revenge: Becoming the Villain in My Second Life

Tainted by a demonic influence, his friend is forced to kill him. But that is not his end. By the whim of a god, he returns in time to where it all began. Yet, in a cruel twist of fate, he is stripped of the memories of his former life and must reclaim fragments of his past by meeting mysterious, hidden conditions. Each piece he recovers reveals a truth more twisted and sinister than the last, showing him that to truly save the future, he may have to cast terror upon the present. — Description from novelcodex.org