Soul Eater.

About Soul Eater

Soul Eater is a Japanese manga series written and illustrated by Atsushi Ohkubo. Set at the "Death Weapon Meister Academy", the series revolves around three teams, each consisting of a weapon meister and at least one human that can transform into a weapon. Trying to make the latter a "Death Scythe" and thus fit for use by the academy's headmaster Shinigami, the personification of death, they must collect the souls of 99 evil humans and one witch, in that order; otherwise, they will have to start all over again.