Yuka raised her adult son Kosuke alone. As he gradually came to resemble her late husband, she developed forbidden feelings that she could only release in private. Kosuke secretly loved his mother as more than family too, but hid it in everyday life. On the night before his wedding, Yuka catches him masturbating and gently strokes his thick, upright cock, saying it is their last night together as mother and adult son. A handjob is not enough for either of them, and their suppressed desire finally drives them across the taboo line.