Masaki, a college student, shares a home with his single mother, Yoshiharu. Their dynamic resembles roommates more than a traditional mother-son relationship. As Masaki observes mysterious marks on his mother's neck after her late-night returns, he questions her supposed work commitments. Despite her denial of any romantic entanglements, the suspicious marks multiply. A chance encounter with his friend's partner leads Masaki to a startling realization when he spots his mother in the company of a familiar figure.