It's primarily meant to be a multiplayer TTRPG, but I suppose you could use it for solo play - you'd just have to do the work of the GM and the player.
That being said, everything in the game from weapon and armor profiles to the various powers and abilities offered by Occupations (essentially the player's class) can be flavored to fit the preferred setting!
I've seen people use it for Metroid games, Sailor Moon, Bloodborne, Warhammer 40k AND Warhammer Fantasy, Bioshock and more! My number one priority was making it super adaptable.