When Mitsuki's mother remarries and relocates overseas, she finds herself alone with her new stepbrother, Yuuya. Feeling abandoned and distant, Mitsuki struggles to connect with Yuuya. However, everything changes when an angelic ghost named Hiyori possesses Mitsuki, urging her to seduce Yuuya to help Hiyori reach heaven. To accomplish this, Hiyori introduces a mystical belt that fills with Mitsuki's romantic encounters with Yuuya. In a bold and unconventional journey, Mitsuki must navigate her complex feelings towards her stepbrother to free herself from Hiyori's grasp and pave the way to peace for the wandering spirit.