Okay so, I know Sburbmod is literally just something I'm pulling out of my ass, but I shall drop some lore. In a similar way to how each Sburb session (allegedly) requires atleast one Space and Time player, Sburbmod requires one Hope Player. This is because, to open the World Lock at the end of the session, the Hope Player must sacrifice themself at the Lazarus Altar, ultimately dooming that player to an inevitable death no matter what (unless there's more than one, in which case only one has to die).

Okay so with that needlessly long ramble out of the way, uh, Orphea was said Hope Player... So yeah, he kills himself, apparently dyes his hair and completely abandons his Limeblood identity. Also he steals Kankri's pants, I'll let you imagine how (It's a colouring error but that's not as fun, now is it?)