A very pleasant incest after a mother and child fight

Chiaki divorces her husband and raises her only son, Junpei, on her own. Junpei has grown so much that he sees a lot of things that are a little difficult to study, but Chiaki is proud of his honest son. One day, Chiaki discovers a test answer in the trash can in Junpei's room with the words "12 points" written on it. Chiaki immediately questioned Junpei, but with a trivial word, the story unfolded in a big way. And then a week from that day...they had not yet been able to hear anything...