My Dear Wife, Mariko's Report

Mariko was found out to have had an affair back when they were newly weds, but nothing major came out of it and they've lead a peaceful married life since then. However, they are worried that their life in the bedroom become boring as of late.
Then one day, Yasushi received a post-cheating sex report from his wife Mariko.
- Her partner is a new employee who is 8 years younger and a virgin.
- He was a long-distance running athlete during his years in school.
- He confessed to her after having sex in a love hotel.
Mariko said that she wants to become his lover and have it officially recognized by her husband.
An absurd demand, but things were different for Yasushi who has a desire to be a cuckold.
He felt intense excitement that he hadn't felt for ages.
Yasushi accepted Mariko's request and her husband-affirmed adulteration began...