I have a theory 4 what's happening n Memoriesofthealhambra .Se joo and Marco were playing the game reached level 90 and no one were killed in reality before. Until someone else know about the game . Maybe wn they gave the game to dr Cha. Someone hacked the game.they modify the game to change the vital signs of the player by effecting their brain in some kind of psychological mind game. That they already can feel the pain as they got injured for real and die. Someone that are close and watching them. that hacker also wn someone died. He modifies the game again & introduce him as NPC in the game.I don't think the game's crazy n itself. I think there's a crazy evil man controlling it. Maybe the father himself or he hire someone to get revenge 4om Jin woo . and Se joo body is the only body is missing . So i think he is the only one is still alive in this crazy game. Like we r facing a murdere in the real world who kill the people and make NPC like them in the game .
I wish he is her friend as he is annoying as hell. I think he will harm hae joo and jin woo in the future. And why he moved with them to Korea .