Naoki began living with his wife and her parents after marriage, but an event drastically shook his life. It turns out Naoki and his mother-in-law, Nana, were once coworkers—and they had secretly shared a night of illicit passion. Over time, their suppressed feelings intensified uncontrollably, and finally, under the same roof, they could no longer hold back. Nana screams, "I can't forget how amazing my son-in-law's touch feels on my breasts!" and shamelessly pursues their taboo relationship even in front of the family. This desire soon brings profound changes to Nana's body.