Just remember that the Kouhai just forced the senpai into the hotel in the first place. Funny how someone who think the other is the worst consent to a relation. The author sure didn't bother to explain how it worked. Magic i suposs. Can't appreciate it when I know how it begin.
Yeah. This one is definitely better without the prequel. Here we see Tougou complaining about her kouhai's behavior, but generally going along with it willingly and even reciprocating, quite strongly, without prompting. (For perspective, ¥10,000 is currently $92.94 usd, which sounds like a lot for a white day present, even if you're a committed couple.) I could very easily believe her resistance here is just an act or a proforma habit.
Conversely, in the first one she's literally blackmailed into having sex and we don't really see anything to suggest it was some kind of role play or false protestation. On it's own, it's bad and, taken together with this piece, casts their relationship in a much darker and more abusive light; one where she only goes along with Sayama and engages in overblown displays of reciprocity as a defense mechanism, to avoid reprisal.
I don't think that's what the author intended and, honestly, this work isn't deep enough to support that kind of story, so I'd much rather pretend the first piece isn't related and they're just a quirky couple with commitment issues.