I dont think Jae Shin(seme) that bad, yes at early chapter there is no consent from the crown prince Nok(uke) but well, Jae Shin is half demon and live at netherworld so his moral will not same as human.
Despite that, he cut (or shapeshift i dont know) his right hand nail short while his left nail still long like a demon is one of the proof he care for the crown prince
He also stopped leaving marks when Lee Nok told him. He sticks to the 3-4 days. But yeah, Its sad there was the one day 7/7 which was the auspicious day and Jaeshin went nuts. He is half ghost. Still doesnt excuse the fact that it's common knowledge buts he's used to treating humans like play thing. Which I love that Lee Nok told him, "I'm not your plaything." Gotta love that man!
what would happen if they want to do...um that thing u know ( ̄∇ ̄")?