So, that part of him matches that in the description of a SAD***. He appears to ‘lack empathy’ as you said, and I think some sadists really do lack the ability to empathize. Because if they empathize, wouldn't it immediately become unpleasant to them? Another point: They like to see people in pain/hurting Remember when MC strained his ankle/leg and he needed Woojins help? What did Woojin do? Humiliate him, pressure him into being “cute" so he'll help him instead of being a decent human lol. In conclusion, Woojin isn't just a "psycho", he's a sad*** for sure. (2/3)