For anyone trying to understand this whole show, here's my understanding (Episode 15 basically summed up everything I tihink)
The way I see it being described is Xu, Yan, Quin, and Hu were all close friends in college. They enjoyed making escape rooms. Yan (the main character), was in love with Xu. Based on other episodes, I'm guessing Xu's dad cheated on Xu's mother. So Yan took revenge by creating an escape room that gave him a heart attack?
Yan has some kind of mental break from the whole experience and forgets who he is. Any recollection of the past makes him pass out and forget everything again.
Xu is upset with Yan for "killing" her father so she teases and toys with him waiting for a good opportunity to kill him once he remembers everything and doesn't black out from it? That's the way I understand it at least.
