Jaa, Kimi No Kawari Ni Korosou Ka?

Jaa, Kimi No Kawari Ni Korosou Ka? summary:

The manga centers on Yūma Fujikura, a constantly bullied first year high school student. When a classmate named Ryō Ameri, nicknamed "Amelie," helps him out one day, Yūma tells him not to get any more involved, or else the bullies will target Amelie too. In response to this, Amelie only tells Yūma that he would commit murder for him if Yūma wanted.