Momoiro Sabbath

From Baka-Updates Manga:
The story centers around a number of witches. The heroine is Kagome, a low level witch with enormous strength. She has for mission to kill Tamakichi, a high school student with a demon soul, and a very unlucky boy. Fortunately she doesn't succeed, begins to like him and becomes his bodyguard instead. Other witches with more magical power also have an interest for Tamakichi, i.e. they want to mate with him because they believe their magical powers will increase when succeeding. This is something Kagome doesn't like of course. Pink Sabbath is a nice comedy, lots of fun.