One of the X-Men's most powerful members, Jean Grey, has officially lost all reason to be part of the team. After her latest battle, Jean was able to accomplish the seemingly impossible goal that motivated her to stay in the X-Men, meaning that she is now free to move on.
As Marvel Girl, Jean Grey is one of the founding members of the X-Men. The initially shy young girl grew to be one of the most reliable members of the team throughout its many incarnations, and a powerful mutant on her own, until the day when the Phoenix Force chose Jean as its host and her life changed completely. The Phoenix is a primordial force of cosmic destruction that consumes entire planets and star systems, representing the cycle of death and renewal. The Phoenix used Jean to take form and destroyed planet D'bari IV, killing its five billion inhabitants. Despite the fact that Phoenix put her in stasis while going on a rampage, Jean still feels responsible for all the death caused by the cosmic force, perhaps due to the intricate relationship that ties them. During the Hellfire Gala, when she was elected as a member of the new X-Men team, Jean said that she wanted to be with the team until she saved as many lives as the Phoenix claimed. That claim may seem preposterous at the time, but Jean managed to accomplish it.
In X-Men #12, by Gerry Duggan, Pepe Larraz, and Marte Gracia, Jean, together with Wolverine, Polaris, and Rogue, assaults Gameworld, the space casino run by Mojo's disgusting replacement, the sentient fungus Cordyceps Jones. Gameworld started running bets on who or what could destroy the Earth, which happened as a consequence of the mutants colonizing Mars. After several attacks from extraterrestrial threats, the X-Men decided to put a stop to it. Jean and the other girls took out Cordyceps Jones, saving not just Earth but many other planets that were going to be destroyed as a result of Gameworld's betting. As Rogue points out, Jean just saved trillions of people, meaning she finally fulfilled her resolution. -Screen Rant
