Mitsuki (Tenka Hashimoto) and Yuya (Yukichi Kobayashi) find themselves as stepsiblings following their parents’ marriage. Mitsuki struggles to connect with her new family, while Yuya is unsure how to interact with his stepsister. One day, Mitsuki is possessed by the spirit of Hiyori (Mayu), who harbors feelings for Yuya and believes he can assist her in reaching heaven. Hiyori fastens a leather chastity belt on Mitsuki, setting a plan in motion to help her ascend to the afterlife.