Ayumi Hizuki, a member of the Hizuki family’s four sisters, becomes entangled in a centuries-old spiritual pact obligating Naoto Rindo to father an heir with one of them. Chosen as a replacement after his fiancée Suzune’s death, Ayumi steps into a role shadowed by lingering grief—Naoto’s accidental use of Suzune’s name strains their fragile dynamic. Central to her journey is a ring Naoto once gave Suzune, now anchoring her soul. When Ayumi wears it, Suzune’s spirit briefly reclaims her body, bridging Naoto’s past and present. Through these encounters, he confronts his loss, forging a tentative bond with Ayumi that culminates in her pregnancy, fulfilling the Rindo family’s cursed legacy while igniting ethical turmoil over Suzune’s potential resurrection.

Years later, Ayumi uncovers Suzune’s survival and aids her soul’s return, despite carrying Naoto’s child. Torn between relinquishing him to her revived sister or claiming her place, Ayumi’s resolve leads to an unorthodox resolution: a polygamous union where both sisters remain with Naoto, each bearing his children.

Academically accomplished and pragmatic, Ayumi earned university accolades while shouldering household duties after her sister Yuiko’s departure. Her quiet, nurturing nature endeared her to peers, though domestic focus and disinterest in romance left her socially withdrawn before Naoto’s arrival. Initially a reluctant surrogate bound by duty, Ayumi evolves into a decisive figure navigating love, sacrifice, and agency amid supernatural legacies, her reserved determination steering familial obligations toward an unforeseen future.