Bae Rona isn't actually dead. Right after we assume Ha Yooncheol was going to kill Bae Rona while she is in the coma, we see a faceless character with leather gloves. The general consensus is that it is actually Logan Lee.

Who killed Bae Rona?

Dante reveals that Ha Eun Byeol killed Bae Rona, and we see a visual of Joo Dante pulling the oxygen pulling the plug in the hospital that fateful day.

Who really killed Min Seol Ah?

In her drunken state, Yoon Hee is revealed to be the final murderer who pushed Min Seol Ah off the 47th floor to open up a spot in Cheong Ah Arts High School so her own daughter could attend.