Oh...

Guwon no, pls be getting sick for some other reason and not bc you kissed a guy. That will literally break my heart.
I think he was experimented on or something and escaped. I feel like someone colored his arms black to cover his original tattoos so he wouldn't have any idea of who he was before. Also he has those weird tattoos on his neck and stuff that looks like stitching scars or staple scars but in tattoo form. Maybe those were originally scars but they were tattooed over to just look like a tattoo so no one would notice that he had like maybe had limbs cut off and put back on? It could of been an experiment to see if he would live with such amputations after being infected. Also he has such unique eyes. How has the MC not wondered about why his eyes glow that silver-white color?
I mean it's not normal that's for sure. I also think there's something weird going on with that town they live in. It's so weird that with all the turmoil going on in the world at the moment that that place is so peaceful. I definitely feel like Guwon has secrets that he can't remember because he was put through some kind of procedure that made him forget. He could have also just forgot cause it was too traumatic but I don't think that's it. I think someone went through the trouble of concealing his identity to the point where not even Guwon would know who he was.