That's how kihoons character is even in the future, Lee yeon doesn't like that he does that and gets mad at him. It's not supposed to be a "cute" trait, it's one of his flaws that even Lee yeon wants him to stop doing.
bleeding during sex does happen in real life btw and they did it without prep + yeon's gargantuan dick i would've been surprised if kihoon didnt bleed.
That too!
im specifically talking about why authors chose to portray such scenes
Why is he bleeding from the behind? This is not pleasant at all. I still have no idea what authors wish to convey by portraying such scenes. That this man can endure any pain from his lover? Why should one serve and pleasure his lover in the detriment of his own well-being? This is not cute at all. I do not like this narrative.