The author set up several things for this moment, he wants this AV arc, and just ignored the character development for it. Kaori getting into the industry as an AV scriptwriter and having a fetish for ntr makes no sense at all, considering how hurt she was when she found out the mc cheated on her. The producer literally told Yoshioka that she’s going to shoot the film of a guy who used to direct adult movies, it was just a way to avoid taking responsibility for her shooting an AV.
The actor himself (the guy who was the hero in chapter 90 when they filmed that sentai movie) hinted at this. The mc has no agency in any of this. It's going to be Yoshioka cheating on the mc(At this point she says that they are not together, so it is not even cheating) just to create drama, and of course Kaori has already picked her actress. Honestly, everything feels so predictable... Just think like an NTR author. oops, that’s exactly what he is. Nothing against the genre, just do it well