magnum

I think Doha is the same entity as the masked killer. Before we got confirmation of the truth of Bada's role in the game, we had some obvious clues leading to it (not being able to kill, always having his clothes and hair changed by a PC, his play being disrupted by the 'anomaly' Doha), but I think the new twist we're learning is not the Doha is an anomaly, but instead that he's THE constant. The killer always kills Seongchan first. What is Doha now taking his time to do as Bada respawns?

Why was the killer always targeting Seongchan first, and why is Doha now fulfilling that role? He has an obvious grudge against Seongchan for what he did to him and Bada. It's also possible that the killer (Doha) has already lived this reality and truth, and has killed his beloved over and over again in a form of twisted assistance.

I think the true end involves Bada piecing together the "truth" and that Doha is the OG masked killer and that it was done as an act of revenge toward Seongchan and his love for Bada. I think he needs to uncover that truth to end the game's loop. I think getting all the desth endings might be a prerequisite to unlocking a true end, which solves the murder mystery.

Also, I think the main player characters are the creators/testers of the game, and Seongchan is the developer, who has just taken it a step too far a la mad scientist, to limit test how realistic and immersive he can make this VR game.

Mayhaps he's an ex-pat like our MC, and simply had to leave Korea when he finished his tour and couldn't get back in. That's the only world in which I would maybe forgive him, or one where he didn't know he had a son until recently, due to a late-life genetic test or something.