Rie was asked by her sister's family to look after her nephew Susumu, reuniting with him for the first time in a while. Susumu, who had long harbored intense curiosity toward his aunt's lush, K-cup breasts since puberty, takes the opportunity of his parents' absence to touch her soft chest. When Rie scolds him, saying, "Susumu, what are you doing! Don't touch your aunt's breasts like that!", he refuses to stop, unable to suppress his desires any longer.