Fuufu Koukan: Modorenai Yoru

"Shall we join them?"
Reiji, accompanied by his wife Kanade and their close friends Kosuke and Asuka, had visited the inn for vacation. On the first day, during dinner, a heated argument broke out between the two couples, and Asuka dragged Reiji away to her room. But from inside, he could hear his wife Kanade's restless sighs...
(Source: Coolmic)
Note: The complete edition with explicit scenes was distributed web via Comic Festa Anime Zone. The on-air version was broadcasted on Tokyo MX and BS11.