きゃん☆フェス！～いたずら魔女とナイショの学園祭～

When the protagonist was small, he took care of a lost witch who would not show her anger even if she was teased. She didn't talk much, but occasionally said “If I get my powers back…” One day she disappeared. Ten years later, the witch Prim comes back and declares that he will now be her servant!

[From Hau~ Omochikaeri!]