A son doted on by his grandmother and mother

Keisuke, the first grandchild for his grandmother Chizuru and the only son for his mother Kiyomi, was loved by both of them. However, Keisuke loves Keisuke so much that his father and Keisuke are in trouble because they constantly fight over him. In order to solve this problem, the parents work hard at night to give birth to their second child. Chizuru, who happened to see Keisuke peeking in, scolds Kiyomi about her sex education, and the two of them compete to teach Keisuke how to have sex with their ripe bodies...