I'm dating a girl who's not conventionally beautiful but has a great personality, and we're starting to think about marriage. But then, we go on a hot springs trip with her best friend couple, and I instantly fall for her friend, Yuna, who's my ideal type. However, I find out she's engaged, leaving me heartbroken. That night, at the mixed bath, I can't resist her stunning body, and despite knowing it's wrong, I forcefully pursue a relationship with her... .