Tatsuya was born when Sayako was a university student. Sayako raised Tatsuya on her own, overcoming the objections of those around her. When Tatsuya grew up, he successfully secured a job, but even at his age he still didn't bring his girlfriend or any of his friends with him. Sayako was puzzled by this, and one night she noticed that Tatsuya was playing with her body. Realizing that this couldn't continue, Sayako invited him to a hot spring inn to have a discussion.