Shikeishuu, Mahou Gakkou nite Kyouben wo Furuu

Taiga Kanaki, who works at the Servaes Magic School, kills for pleasure. Every day he enjoys his "hobby" and smiles at students who adore him. Everything is going well until he decides that a new student is his next target. Just like that, Kanaki's life begins to unravel... This is the story of a psychotic killer who toys with life using magic.

(Source: Amazia, translated)