Usi's story is kind of interesting. The husband has ED so he and his wife haven't had sex in a while. The wife meets her ex-boyfriend by chance and has some coffee with him; the husband saw them and assumed the worst. Later, the wife decides not to say that the man was her ex-boyfriend, but it doesn't seem to matter: the husband reveals that after seeing her he kept imagining his wife fucking another man and got both angry and aroused. The husband forces her to recount her sexual encounter with that other man, and the wife does so to keep him excited -- even though she never slept with the other guy. At the end of the chapter, she indicates that she's going to search for other ways to keep this up, as she loved the hard sex.
What makes this really interesting is that it's entirely from the wife's point of view. I hope it doesn't go full NTR like Cuzukago's previous work that started in a similar fashion. I'd prefer a series where the wife thinks up elaborate ways to wind her husband up for some hard and faithful sex. Usi likes threesomes and group sex, though, so we'll see how it all goes.