WARNING: The following contains spoilers for X-Men #18 by Jonathan Hickman, Mahmud Asrar, Sunny Gho & VC's Clayton Cowles, on sale now
Mutants get their powers as the natural result of evolution, but some of the X-Men's greatest enemies are not content to let nature take its course. Several groups of humans over the years have tried to give themselves mutant-like abilities, among them the Children of the Vault, a group of humans who have evolved powers of their own through time manipulation.
After the mutants formed their own nation on Krakoa, the X-Men discover one of the Children of the Vault named Serafina at a facility run by the anti-mutant group Orchis. When Serafina flees, Professor Xavier sends a team to pursue her. In X-Men #18, the team finally make contact, killing several Children of the Vault in a blinding flash.
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The three-person team that Professor X sends after Serafina consists of the new Wolverine (Laura Kinney), Darwin and Synch. In X-Men #5 they enter into the Vault, a sealed environment where time flows at an accelerated rate, allowing the Children to evolve over the course of millennia in what is just a matter of months or years to the world outside. Wolverine's healing powers and Darwin's rapid evolutionary abilities allow them to cross the threshold of the Vault without being harmed by the different flows of time, while also enabling them to survive inside the massive time-displaced city. Synch can copy another mutant's powers so acts as a redundancy, but in X-Men #18, his powers level up and he kills the Children of the Vault.
The Children have been a constant presence in Hickman's X-Men run since it began, when Serafina was discovered as an apparent prisoner in the Orchis base. She has numerous powers, including the ability to cloak herself from being detected either by telepaths or the human eye, and she can also control almost any machine she encounters. Additionally, she can dominate people's minds. Her fellow companions include Sangre (who creates bubbles from moisture in the air), Perro (who manipulates gravity), Aguja (who can create force fields and unleash blasts of energy), and Fuego (who is pyrokinetic). With these powers, the Children of the Vault have evolved specifically with the intention of inheriting the Earth, and Xavier even called them an existential threat to mutants.
Serafina is in the middle of syncing her body with the Vault's computer systems when the three mutants are detected. She rallies her companions to defend the city, and Fuego tries to burn the mutants. However, Wolverine guts Serafina, but Fuego unleashes another fiery blast and ignites Synch. At this point, Synch demonstrates a new level of his abilities, suddenly copying Fuego's pyrokinesis. the first time he has ever copied the powers of a non-mutant. This suggests that, like the Children, he too is evolving.
With his new power, Synch takes the last of Fuego's heat, then hurls a fireball at the other Children of the Vault, killing Sangre and Perro. As the only one left alive, Aguja tells the X-Men that they can stop her, but they cannot stop the future. Then she explodes in a massive ball of energy so powerful it swallows half the city.
Wolverine, Darwin and Synch entered the Vault as part of a fact-finding mission, but it was always likely they would have to use lethal force. While they can be resurrected once they escape and have their consciousnesses transferred to new bodies with the information they obtained, Aguja's energy attack is a perfect example of why the Children of the Vault pose an existential threat. But given the sudden evolution of Synch's powers, it seems that mutants are actually the ones destined to inherit the future.