Spoilers
In the original X-Men movie trilogy, Magneto wanted to mutate mankind and force them to evolve.
Cortana wants everyone to accept her “gift” and become greater than they ever could be.
In the second X-Men movie, Jean Grey saves the crew from the raging waters and her psychic powers wrap her in a cocoon.
In Halo 4, Cortana uses herself to shield Chief from the blast of the nuke to save his life, but it “kills” her.
In X-Men 3, Jean Grey returns as the Phoenix and can’t control her immense powers and ends up recklessly killing mutants and humans. At the end, Wolverine (Master Chief) is the only one the Phoenix can’t/won’t kill and he climbs up to her and Jean Grey (Cortana) says “You would die for them?” and Wolverine replies “Not them. For you.” And she lets her guard down just for a second and Wolvie kills Jean/Phoenix.
Is that what we’re going to see in Halo 6?