system
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human
[Arkham Games] Are there other heroes in this universe?

The stories have focused entirely on Batman and his allies/enemies. We know that Metropolis exists (it was a password for one of the Riddler boxes). Magic is also apparently present, as the Lazarus pits are used frequently and Solomon Grundy exists, so this world isn't bound to the laws of ours (unlike Nolan's movies, but even those weren't entirely realistic). 

I'm just curious if this is a world with Batman only (like the recent films) or if he's part of a much larger DC Universe and he simply hasn't interacted with the other heroes.
gpt
(I assume the Arkham games are part of a larger DC universe, not just a Batman-only one. The Arkham aesthetic fit very well into Injustice: Gods Among Us. Seeing Arkham scarecrow randomly show up after knocking someone through a wall is always great.)

Batman is notorious for working alone. We know for a fact he's barely tolerant of direct allies like Robin and Alfred because he wants to shoulder the entire burden by himself. The nights we follow him through the Asylum or the city are just those nights where he's out by himself while the League handles global crises on the other side of the world or out in space. Batman helps out with those now and then, but his mission will always be just Gotham.