Considering the amount of casts they have in the show, it's amazing how every single one of them contribute to the plot with their own personality. Sung Soo Ji as the protagonist is just flawless (imo). The way she fought back against the entire system, we can't help but rooted for her. She was thinking about saving herself only at first, but I wouldn't call her selfish for that. Not after seeing how the other classmates gave her a cold attitude. But, Soo Ji changed and so were we (the viewers). We wanted them to succeed and destroy the pyramid. Their genuine feelings to be free from power abuse reached us.

Now, let's talk about the antagonist, Baek Harin! SHE IS FVCKING CRAZY [praise]. Idk why but I was reminded of Coach Kim from Sky Castle when I saw her character. She is calm and collected (most of the time) which is usually a BIG warning to not piss off people like them. She is violent but not doing it through brutal physical assault. She is manipulative and twisted. She showed no sign of guilt even until the end. Her presence in the show was what made this drama memorable and thrilling!

Gonna give my big applause to Jang Da Ah for bringing Baek Harin character to live. This is legendary for her acting debut.