Touya Senji has spent his whole life chasing excellence and coming up empty. No matter what he attempts, talent eludes him, and growing up behind a gifted older brother has left him with little confidence. Turning to schoolwork as a final hope, he keeps ranking among the top hundred on national practice exams but still feels unfulfilled. Everything changes when he meets his classmate Haito Luo Buffett, a kendo champion and a Returner who draws on the abilities of her past lives through the Stem of Reincarnation. The catch is brutal: the power only works when she slits her own throat. Touya first crosses paths with her while she battles a serial killer, and before long this protector of humanity wants him to join her. The result is an action series built on a supernatural power with a grim cost.