Okay so this might just be me picking up on common tropes and certain things they left in so it might be a spoiler but I have no fore knowledge past the current latest chapter which is 29.
I swear to god Doha is the main villain. Like he controls this world in some way. In the beginning he doesn't have free will like he was this programmed big bad. The game is supposed to work by the guys figuring out together with maybe one or two dying that the murders that happened nearby were orchestrated by the villagers and that one of the family members escaped from the slaughter ( Doha ) and that the villagers were the ones who slaughtered his family and then pinned it on him.
His family were probably part of a cult or some kind of nefarious group with the villagers but the other villagers asked his family to sacrifice a kid or some shit after prolly sacrificing animals and dead bodies previously. The family disagreed so the villagers attacked them. When Doha, Bada and the group come over they plan to sacrifice them. ( this whole family cult thing is shaky and may or may not be true I am not committed to the idea).
The killers who respawn are these villagers, sending in a new contact when they haven't heard from one in a while.
I don't know how this groundhog / game world started but note how we haven't seen Doha die yet. Like not once. Bada either dies first or separately and we only hear from Doha how he dies. Kinda like he isn't actually dying just restarting the loop so he can be with Bada again. He gained this sort of free will when Bada saw him kill a villager, and the next round he found out about the game and copied Bada with the second tape allegedly. I think he might not have had a tape but just pretended to see what Bada would say. And when the next round he remembered Bada accused him of putting in the tape he found out what it did by lying about doing it. He then continued to learn from Bada about the world he couldn't remember.
Unlike the guy who vaguely remembers and his bf he doesn't ask why Bada just ran away. Sure he knows Bada has died before but he doesn't know if he's tried to escape the moment he wakes up. Kinda like he doesn't need to know. He has control over the game world and doesn't actually want Bada to leave because presumably something caused this world to exist and Doha doesn't know if he will be able to get out of it. Especially if he's in fact the one who controls the game ( to a certain extent he doesn't control the villagers or the clues appearing he just controls the loop and has the ability to add in a new feature like the new "DLC" and the other cassette player) he might not be able to get out. And he want's Bada to stay with him. Think about it his death never added a new ending after the first one. I suspect he can only control things he knows about or things he can interact with past a certain point.
I think this also explains his interaction with the guy who vaguely remembers. He wants to test how much free will the others might get. I mean if Bada remembers everything in the game what makes him different to the other guys. I mean why does he remember and keep things from past iterations. What happens if the others find out about the game he want's to test out the others ability in the "game". Will what made Bada interesting be unique to Bada. Not realising that Bada also has experience and a mental fortitude built out of trauma and repeatedly doing this game over and over. Though whether Bada is unique or not might give him a clue to how the world works too. I mean there has to be an actual reality too and clues to their interactions to the game world and how they experience the game world may play to how they are outside the game world too.
Bada being familiar with the study room in the abandoned house is also suspect. He might actually be part of that family or remembers it from before he was pulled into the game.