OBA-321 A married woman named Yagi Michika invites her lover to her home and indulges in sex while her husband is away.

Michika, her son, and her husband have decided to go to the concert of the popular idol group "Puri Puri Princess Z" this year. The night before, while looking forward to her concert, she and her son were dancing to a popular song by Puri-Puri Princess Z, when Michika received a phone call. The owner of the phone was her younger sex friend, Kenichi, whom she met at a part-time job. And on the day of the concert, Michika pretends to be sick to break her promise to her son and her husband, and brings Kenichi to her house where no one is there...