One day, Yachi Haruaki was sent a black cube by his father who is on a journey. The black cube is actually a cursed tool which absorbs negative feelings until it turn into human. Fia, the black cube, then live in Haruaki's house, while Haruaki & Muramasa Konoha(also a cursed tool) teach basic knowledges for daily life to her. She is also doing good deeds in order to remove the curse on her. But Peewee Halowie, a member of curse destroyer organization, appears...