Boku ni Korosarero

Yuu Yakushimaru is a high school boy who has been skipping school, instead spending his days hating on his bullying classmates and unsympathetic teachers, and dreaming killing them all some day. When he gains the "power to kill" and discovers that the people he hates are actually monsters, the killing spree won't stop! And so begins a story of non-stop horror and suspense!

(Source: Comic Days, translated)