At the Isshiki household, daughter Kayo got married and began living with her husband Masato at her parents' home. Since Masato often worked from home, he became a dependable presence for full-time housewife Momoko. One night, during a dinner just the two of them, a drunken Masato made Momoko flustered, and she impulsively kissed him. When Masato awoke to the moment, he was stirred by Momoko's mature, voluptuous body. Overcome by uncontrollable desire, he forcefully took her lips. In that instant, they crossed the line—swept away by mutual passion, they plunged into an irreversible, deeply intimate relationship.