My wife's secret: My wife doesn't know what I know...

Masayuki, the older brother of her husband Kazuhiro, failed at work and lost everything, and ended up staying there for a while. Although his wife Mako is confused, she accepts her husband's suggestion... Masayuki, who has not been divorced for a while, knows that he is his younger brother's wife, can't control his excitement just because there is a woman under one roof. Mako is troubled by an infidelity with her brother-in-law, and spends her time worrying about Kazuhiro noticing him, but Kazuhiro, either knows or doesn't know, treats Mako in the same way as usual...