What do you mean manipulated? He did that of his own free will
If I'm remembering correctly, Heesu has mind control abilities. Although it's not completely clear, it did kind of seem like Heesu was controlling Chan's mind (and actions through it) and he was only released after the other insane guy ejaculated inside Yugeon. At the same time, however, Chan did not seem like he cared enough to stop Heesu from continuing (hence walking away). He just seemed disgusted with himself.
Honestly, that self-focused mentality is very on-brand for these bastards. None of them seem to actually care for Yugeon, rather how they feel in whatever situation or moment they're experiencing. ┑(￣Д ￣)┍
i felt like he was "being rough" bc his mind was clouded with thoughts about yugeon running away (or maybe jealousy bc of taein? or both? idrk) and that he came back to his senses bc he heard yugeon screaming
I KNEW IT CHAN WAS MINIPULATED ... I wish he would have stopped it after he realized