A used apartment in a certain city in the Kanto region, aimed at families. The 'Hayama couple' and the 'Hoshino couple' live on the same floor. Both couples have been married for five years, have children, with husbands working full-time and wives part-time. Due to their roughly similar age, both households have been interacting as neighbors. "Yamazaki's wife Sayuri" and "Hoshino's husband Akira" had a secret they could never tell. In fact, these two were married individuals living in the same apartment building and had fallen into an illicit affair.
