I don't know what moved into my futon

One day, Yachi Haruaki receives a big black cube from his father, who works overseas. Overnight, the cube morphs into Fear, a tsundere loli who has turned up to remove the curse placed on her through accumulating negative emotions. At night, Haruaki encounters her stealing rice crackers, and allows her to stay at his place, much to the horror of Konoha, Haruaki's childhood friend.