Magma is a new inductee in Xavier's school in the game's storyline and is depicted as an American girl under the name Alison Crestmere. She was first seen being dragged away by a soldier working for the Genetic Research and Security Organization when Mystique and Blob of the Brotherhood of Mutants arrived to claim her. She was saved by Wolverine and Cyclops and taken to the X-Mansion where she quickly became a student.
Professor Xavier offered her (and she accepted) a spot as the newest member of the X-Men team. It was later revealed on Asteroid M by Mystique that she was their backup plan to power the Gravitron should the Brotherhood fail to rescue Magneto. While not initially usable in missions, she becomes a prominent member of the team and a vital key to victory.