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My guess is that eyeglass guy is manipulating Bada to have progress in the game without eyeglass being involve directly or putting much effort. In gamer term its like Bada is carrying him without even knowing lol. So the eyeglass is the other player not Doha, but still doesn't explain why Doha was talking in the earlier chapters with a stranger and killed him as an NPC (it was the first time Bada did it without outside trigger).
My another guess is that anyone who keeps their memory/identity as player in the last session of the game is the only one who will survive. So not only the player/s needs to find all ending but they also need to wary of the NPC, because once the NPC load the new cassette tape they will be a new player. Worst is that if an NPC overrides a cassette tape will be the new player, and the original owner who saved the cassette tape from prev session will be the new NPC unless he find another cassette tape to load/save. So its like, loading a already owned/saved cassette tape is stealing the identity of the owner as a Player. Hence, why Doha have awareness in the next session after being killed in the session where he load the cassette tape of the eyeglass guy.
Also supporting this theory is that the after Doha became a player by using the cassette tape of eyeglass guy, the eyeglass guy memory is stuck. He only members until last session of his saved. I guess he didn't know Doha is now a Player because, Doha became a player after eyeglass guy last saved. So every new session his last memory is always his last saved.
But I still believe that Doha is a player even before he saved the cassette tape, he only joined the game in the middle. (You can browse my previous theory here about this lol)
I'll wait for the next chapters for more theories hahahaha.