Anne Freaks

While trying to bury the body of his mother deep in the woods, high school student Yuri is approached by a strange girl who offers to help him. That is... if he promises to be her "parent killing assistant." Meet Anne Freaks, a bright, attractive teenage girl normal in every way—except that she's on a mission to kill her father, the leader of the dangerous extremist cult: the Kakusei Group.

(Source: ADV Manga)