A Dark Rabbit Has Seven Lives - Season 1, Episode 10: Spirited Classmates

Kurogane Taito is a freshman in Miyasaka High. After an injury in his leg(snapped tendon) that prevented him from practicing karate, which he excelled in since elementary school, he had always believed that he was an ordinary, regular guy. However, due to a forgotten promise exchanged with a beautiful Vampire (Most Ancient Sorcerer) Saitohimea nine years ago, he was in fact no longer ordinary. Nine years ago, he was injected with Saitohimea's poison, which prevented him from dying as long as he didn't die seven times within fifteen minutes. Shortly after his change, A boy named Kurenai Hinata attacked them with a demon and killed Taito six times. In order to prevent Taito from dying, Saitohimea agreed to leave with Hinata and have Taito's memory wiped. As a result, Saitohimea was experimented on and imprisoned within a world with no sound or light whatsoever, and Taito continued with his life as a normal human until his freshman year in high school.