Reincarnation no Kaben

From Mangamo: Toya Senji is talentless. He's tried everything but he can't seem to excel at anything, no matter how hard he tries. Then he meets Haito, a Kendo champion and humanity's protector? She uses the Stem of Reincarnation to draw on the abilities of her past lives, but it only works when she slits her own throat. And now she wants Toya to join her?