Ritsuko is a virtuous wife who lives with her son and husband.
One day, her son's best friend, Ryo, comes to her with a serious look on his face and hands her a DVD.
The DVD shows her son, Takeshi, and Ryo's mother having an illicit affair. Ryo looks overwhelmed.
"You treat my mother like a bitch! I'm going to fuck you and make it even!" He shouted.
He attacked Ritsuko.
Ritsuko accepts Ryo's body out of guilt and pity, but she soon finds herself drowning in his young body...

(Source: Magazine Magazine, translated)

1-3. Kirishima no Haha-chan Kanrerutte yo (桐島の母チャン姦れるってよ)
4-5. Boniku Koukankai (母肉交歓会, Boshi Koukankai, 母子交歓会, Oyako Koukankai)