Who is the S-class hunter?

After ten years of suffering through illegal research experiments, Sion suddenly awakens as an S-class. To grant a request from his friend Johan, he destroys the laboratory and heads to Korea... --- “Baby, you know you aren't allowed to break the S-class training room, right?” “I-I wasn't going to break it... I really don't know why it ended up like that... The machine just broke on its own. I-I'm telling the truth.” “Yeah, you really shouldn't break it. It's very expensive. If you want to pay for it, you'll have to work incredibly hard, baby.” “Uh... uh...” Sion fidgeted restlessly, shifting his weight from side to side. Cha Yu-seong, who was about to tilt his glass, turned ...