Theories

Joshua is from the Sentient Genesis/ Is the Sentient Genesis
Facts to support:

- He claimed to be as old as Excellion (Living from even before the multiverse was a thing)

-His power is immense, god knows if it even is more powerful than Excellion. It is clear that he didn't fight for real on the fight against the group, because he wanted to know their ideology after the game.

-His body is literally a lightbulb which sometimes represents the holy and divine.

-Excellion and him seemed to have already known eachother, even before the Reaper's Game.