Petals of Reincarnation

Toya Senji appears talentless; no matter how hard he trains, he can't seem to excel at anything. His fortunes change when he encounters Haito, a kendo champion and, astonishingly, humanity's protector. She channels the Stem of Reincarnation to tap into the powers of her past lives, but the ability only activates when she cuts her own throat. Now she wants Toya to join her.