Itsuka Tenma no Kuro Usagi

Miyasaka High freshman Kurogane Taito. He had excelled at karate since elementary school, but after suffering a leg injury (a snapped tendon), he has always thought of himself as an ordinary, everyday guy. However, he is actually no longer average because of a pledge he made to a stunning Vampire (Most Ancient Sorcerer) named Saitohimea nine years ago but has since forgotten. Saitohimea gave him an injection of a poison nine years ago that keeps him from dying as long as he doesn't pass away seven times in the space of fifteen minutes. Soon after his transformation, a young man by the name of Kurenai Hinata ambushed them with a demon and swiftly murdered Taito six times. Saitohimea agreed to go with Hinata and let Taito's memories to be erased so that he wouldn't be able to kill Taito directly. Following this, Saitohimea was subjected to experiments and imprisoned in a dimension devoid of any sound or light, while Taito carried on with his life as a typical human.