This article contains spoilers for A.X.E: Judgment Day #4
The Eternals and the X-Men are becoming one through a union never before seen in Marvel Comics - and this has massive implications for both groups moving forward. Both species are engaged in a bitter war in Marvel's new Judgment Day event, and the conflict eventually puts the entire planet at risk when a Celestial awakens to threaten Earth. But A.X.E: Judgment Day #4 reveals the threat can be stopped by the X-Men, the Eternals, and their new and dangerous union.
The event, which began with an Eternal invasion of the X-Men's island of Krakoa, took a turn for the worse when the Progenitor Celestial (formerly an Avengers base) awakened and decided to judge everyone on Earth. Humans, mutants, and Eternals are judged individually and as a group; many see a thumbs "up" or "down" from the Celestial (who often appears as the person whom the accused most admires). If found lacking, the Celestial will destroy all - and every attempt at negotiation has failed. Thus, the Avengers (stuck in the middle of the conflict) attempt to destroy the Celestial - but that ends in failure as well.
In A.X.E: Judgment Day #4, written by Keiron Gillen with art by Valerio Schiti, the rebel Eternals (who have sided with the X-Men and wish to stop the war) hatch a plan: replace the Prime Eternal Druig with Eros, who can then use his power to stop the Progenitor Celestial. In order to do so, Eternals modify the firewalls of the Uni-Mind, the great meeting place of the Eternals (which also doubles as a weapon). With safeguards disabled, the X-Men enter the Uni-Mind alongside the Eternals, becoming one mind and one entity. Eros is quickly voted in as the next Prime Eternal.
While the union is temporary, it is also a watershed moment in Marvel Comics: the Uni-Mind was strictly for Eternals, not mutants. But the X-Men have bridged the gap and journeyed into the Eternals' most powerful location. At the same time, the Deviants are officially recognized as mutants by Krakoa, allowing them to pass through the many gates to the island paradise. The boundaries between mutant and Eternal shrink with every issue, and the two groups now have more in common than ever before...especially when one considers resurrection.
Both mutants and Eternals can return from the dead an unlimited number of times, but there are downsides that cannot be avoided. Mutants can lose their memories if their mind isn't regularly backed up by Professor Xavier's Cerebro, and a human must be killed whenever an Eternal resurrects (it is the darkest secret of the Eternals and most are not even aware of the sacrifice). The X-Men and the Eternals' bitter war will end with one side remaining - but it may be an amalgamation of both.