I'm getting the impression that at least one of these girls is going to go to the yandere side. The 'MC' doesn't seem to be, or just doesn't care about the future reactions/behavior of these girls after he's used them; Fuyushima probably isn't going to become into him, but 5xSex sensei certainly is, and I'm really curious to see if she actually witnessed his latest scene here. At the least, wouldn't she become suspicious as to why these two students are staying after school in the classroom alone together? Maybe the author is invoking some hentai logic here, where all of a sudden the other students and staff just vanish when the final bell rings, but I think it's only natural that Harumachi would be paying extra attention to what Saino is doing while in school.