When her mother remarries, high schooler Mitsuki Kanzaki gains a stepbrother, Yuuya, and ends up living alone with him once both parents move overseas. A ghost named Hiyori, unable to pass on, possesses Mitsuki's body and steers her toward Yuuya, using a special belt that fills up whenever Mitsuki's feelings for him tip into romantic territory. Hiyori needs the belt full to finally reach the afterlife.