At the beginning I really believed that Yeonhwa changed. Well, it seems she is not a psycho anymore, but in the end, she is not that different, I mean she still doesn't give a fuck.
That's why I was pissed at the end of the prequel too, after all that happened, she still didn't care.
Btw, It would be funny to see them meet with Ayeon and his current gf. What a shitstorm would that be, heh.