There’s a lot more extreme bdsm stuff than scat… he could be inflated, enema kink, fisting kink, cuck kink, piercing kink, needle kink, cutting kink, etc. And you say that a manhwa wouldn’t but I’ve seen all of the above in a BDSM yaoi manhwa and this is a BDSM ecchi Josei(?) manhwa so I don’t think it’ll be that different in terms of what you can and can’t show.
Proof
I don’t think any of those things are more extreme than scat lol. Scat is usually the biggest squick as far as sex acts though because it’s so unsanitary and gross.
… people think we will get scat in a manhwa, LOL. The worst a manhwa would do is watersports.
But I’m pretty sure that it’s just going to be good ol’ pegging.
Also, seeing Richard cross-dressing unlock a new desire in me. I want him to get to indulge his clear exhibitionism kink but too bad he’s a crown prince.