This topic may contain spoiler
As far as I understand:
The closed beta was going to be human experiments (probably to get the right level of realistic). Which the brother found and probably to leave evidence made into a very hidden dungeon.
The human experiments really happened to the younger brother (zodiac). And either to get stronger, to get the evidence zodiac needs or to find a trace of the brother's whereabouts he went back into his one personal hell (the experiments).
The experiment is probably exactly as shown. As normal of a situation (being a doctor at a hospital) turning into a painful monster fest to get genuine emotions.
The experiments are probably also why zodiac had scars and can't feel pain. And he just wants someone to relate to I think or he remembers other people in the closed beta, but doesn't know if they were NPC or players or if the players even survived. (I suspect he's the only survivor)
Wait let me get this straight the data which is human experiments was made into a dungeon and hidden and zodiac’s brother was the one who collected it?