Ai Suru Tsuma, Mariko no Furin Houkoku: Otto Kounin no Gachi Furin Sex

The protagonist Sashihara Yasushi and the heroine Sashihara Mariko have been married for 5 years. 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...