The game starts as your character is forced to become an AGE (or Adaptive God Eater), a human who’s been biologically bound to a giant weapon.
The world in God Eater has been overrun by monsters known as Aragami, and weapons—called God Arcs—are the only instruments capable of slaying them.
In fact, God Eater 3 on the Switch emphasizes co-op play as the ideal way to play the game, but it does not go out of its way to require you to play the game as such, since I was able to play through Story Mode and ancillary missions without feeling like I needed to find a partner, though it does make certain missions much easier to complete and rank higher if you do.