Yuka's husband passed away in a traffic accident, so she raised Kosuke alone. Kosuke is a writer, he seems to be rewriting a work about his feelings for his mother. His feelings for his mother go beyond maternal love, but he always hides his true feelings. The same goes for Yuka, as Kosuke becomes more and more like her late husband, causing her feelings for her son to gradually change to the wrong kind. The two continuously masturbated thinking about each other, each time they deliberately opened the door so the other could find out. Even so, the two have never crossed the final boundary of morality. But on the night before Kosuke's wedding, after confiding in his mother, Kosuke returned to his room to continue writing his novel, but he couldn't control himself and masturbated thinking about his mother. This time Yuka no longer stood by and watched, she went into the room and wanted to be with Kosuke. The two expressed their true feelings and gradually crossed the final boundary...