Rockwell + Gangster

Melissa is a young, not very powerful witch, whose magical contract is with a demon in the form of a cat, Yorun. Her teacher takes her own life, due to personal reasons, and Melissa wants to find a way to bring her back from the dead. For help, she summons the great legendary hero, Shade Gangster, though his real identity seems a bit shady. Together, they begin their journey to find the resurrection spell, facing many supernatural dangers along the way.

(Source: MangaHelpers)