Hope/Rogue
Some of the Avengers went to the moon to try and stop the Phoenix, and the X-Men followed. Five of them ended up taking in the Phoenix: Scott, Emma, Namor, Illyana, and Piotr. They were never meant to have that kind of power, and they made Earth a Utopia for a little while....but then they did terrible things with it, Rogue. So many of us died, Avengers and humans, too. Namor decimated Wakanda. As each of them fell, their powers went into those remaining. Scott ended up the last, and killed Xavier, becoming the Dark Phoenix. Wanda and I fought him and defeated him, and I became its host. I fixed the world and restored mutantkind, then released it.