the danger for mc is this dynamic continues forever where she just turns into cat at any time and he can't help but let her have her way. all the way to the altar lol
but that's not too different from the normal male female condition, so if we're exploring human nature under a fantastic lens... does that make this manga sci fi?
Please refer to the story of an irl guy who got his dick stuck in a stray cat, which he tried to fuck while drunk (I think it was posted in 4chan, but I may be wrong). He caused the cat to have internal bleeding, and caused the cat to bleed out when they had to perform surgery to get it out.
That should give you a horrifying visual on what may happen if she transforms into a cat while they are banging. Good luck recovering from that image.