Uriel and Eimin were born in furtherance of the goals of progressive evolution. The Celestials are a race of cosmic entities dedicated to keeping evolution continuing apace on worlds such as Earth. To ensure this goal in their absence, they empower a Celestial Gardener from among the dominant species to champion the cause of evolution. A Gardener can in turn empower their potential successor or successors should they fall, typically through Celestial bio-technology known as a Deathseed. The death of the Celestial Gardener En Sabah Nuhr led to the forced ascension of his former Horseman named Warren Worthington III, or Archangel. Archangel was
effectively killed by his former allies in X-Force during his pursuit of evolution at any cost, when they used a Celestial Lifeseed to purge his body of the enhancements and drive provided by the Deathseed at his core. Before his reincarnation as the Lifeseed's Angel, however, Warren had conceived children with Ichisumi, the Pestilence of his Final Horsemen. Clan Akkaba fled from Archangel's failed scheme in their Celestial Ship, preserving the madonna and the heirs to Apocalypse. [Uncanny X-Force (1st series) #11-18]
Pestilence eventually gave birth to twins, whom she named Uriel and Eimin. These children were destined to rise and claim the role of Celestial Gardener, but this destiny rankled the time-traveling conqueror known as Kang. The warlord had failed across numerous timelines in trying to conquer the mutant race, always rebuked by the mutants' chosen guardian of evolution. Even if the Apocalypse Twins fell, another Gardener would rise, an eternal cycle that opposed Kang's plans indefinitely. Instead of fighting the twins directly, Kang decided to enact a more subtle scheme that required him to commit to a long game. Shortly after their birth, Kang infiltrated the stronghold of the Clan Akkaba and kidnapped Uriel and Eimin, planning to indoctrinate them from birth in his own views on human/mutant relations. He would manipulate the twins' development so that their natural mutations would be augmented by his own chronal powers, given them new temporal abilities so long as they remained together. [Uncanny Avengers (1st series) #5]
Kang raised Uriel and Eimin with his ideas on strength and "honor," coupled with lies about his own greatness. Kang claimed to have killed the Twins across countless realities, but had chosen to be magnanimous in this timeline. Growing up, they were educated by the conqueror in the belief that man and mutant would never live together in peace. For emphasis, Kang sent Uriel and Eimin to live in the mutant concentration camps of the Red Onslaught, a few years from their birth in the immediate future. As children, they were tortured and abused by the mutant-hating cyborg Ahab, who ran the camps in secret alliance with Kang. On one occasion, the Twins attempted to escape, only to be betrayed by a human ally. Ahab and his Hounds captured the Twins before they even got out of the camps. When Eimin took the blame for instigating the escape, Ahab forced Uriel to take his sister's eyes, blinding her, or else watch Ahab kill her in front of him. Kang used this lesson to impose upon them that humans could never be trusted. [Uncanny Avengers (1st series) #12]
A few years later, Kang retrieved the twins from the camps to continue their tutelage from his distant 42nd century home. Kang's ultimate plan for the Apocalypse Twins was for them to conduct a Rapture, ascending all of mutantkind from Earth to go and settle some distant star system, giving them a form of peace while also removing them as a nuisance to his conquest. As a conqueror across time, Uriel questioned why Kang didn't merely eliminate his rivals as helpless children. Kang instructed the twins in his views of honorably facing a foe on the battlefield, earning the kill rather than merely removing an obstacle. He also made a small tangent to point out the unintended consequences of killing one's foes through time travel. The early death of Reed Richards, for instance, would mean Galactus would be unopposed to consuming the Earth, wiping out Kang's own future empire. As Eimin and Uriel pondered that paradox, Kang also bragged about his arsenal of trophies, such as the Asgardian axe Jarnbjorn, enchanted with the power to slay even a Celestial.
To give the twins a chance to begin seizing their own trophies, Kang arranged to drop the adolescent mutants into the present. A temporary paradox due to others time traveling had created a timeline that would soon end, an ideal hunting ground for the Apocalypse Twins to test their mettle. Uriel and Eimin hunted Steve Rogers in the Morlock Tunnels, where he attempted to negotiate with Havok and Rogue, the Morlock leaders in this reality.
The Twins pursued their goal primarily to avoid the consequences of failure at Kang's hands. Uriel hesitated, however, particularly when Rogers was injured only because he saved mutant lives from Uriel's own impulsive attack. Kang urged him on, and Uriel ultimately made his first kill by slaying Havok when the mutant stood between him and Rogers. Rogue was furious at the death of her husband but, when she touched Uriel, her power showed her what he had gone through, and the abused boy earned her sympathy. Rogers had run off by this point, so Uriel tried to argue his view point with Rogue, and attempted to get her to a Morlock healer rather than let another mutant die at his hands. Instead, Eimin mercilessly killed the woman in Uriel's arms at Kang's direction. A furious Uriel tried to defend the strength he had found in showing mercy, but Kang laughed off the idea and stated Uriel only showed his own weakness by thinking so. He prepared to send Uriel back to Ahab's camps to learn his lesson, and Eimin stepped forward to share in her brother's punishment. [Uncanny Avengers (1st series) #8AU]
As the twins reached adulthood, they plotted in secret for ways to turn the tables on Kang for a lifetime of abuse. Eimin's time-space synesthesia allowed the twins to trace the outcome of different strategies and learn from mistakes without actually making them. While Uriel's active chronomancer talent made him more powerful, it was this gift that made Eimin the true mind behind the twins' plotting. Despite everything he had done to them, Kang had truly convinced the Apocalypse Twins that man and mutant could never live in peace together. Building off of Kang's lessons, Eimin saw a way to rob Kang of his prize while still providing sanctuary for their people. Uriel agreed to Eimin's plan as she explained it to him, and the twins armed themselves to return to the past.
Using hyper-augmented Pym Particles from Kang's treasure trove, the Apocalypse Twins first formed the Akkaba Nebula, an entire microscopic solar system with multiple entry points on Earth, allowing them free access to their birthworld from an otherwise undetectable location. From their ship they broadcast the power of the tachyon dam. Arriving in the past months before their own birth, the dam stabilized the timeline and prevented other forms of time travel from interfering with their work once it was activated. Their actions would now cement the inevitable future of the timeline forevermore. All this was intended by Kang's original Rapture plan, but Eimin added one final wrinkle: Jarnbjorn.
With the power of the Celestial-killer enchantment on the axe and his own chronomancer ability, Uriel and Eimin were able to assassinate several Celestials throughout the cosmos. In doing so, the Apocalypse Twins acquired a set of four Lifeseeds and Deathseeds from the corpses of their victims. Earth's super-beings Banshee, Daken, Sentry and the Grim Reaper were first resurrected using the Lifeseeds and then transformed into the Four Horsemen of Death using the Deathseeds, each one intended to play a different role in the conflict Eimin foresaw with the Avengers Unity Division over the Rapture. Perhaps out of symbolism, the Apocalypse Twins appeared at the anointing of Genocide as the new Celestial Gardener, and killed the Celestial patron who offered him a Deathseed. The scion of Apocalypse tried to claim the role after the disappearance of the infant heirs of Archangel, and so Uriel and Eimin removed Genocide, War, and Famine from their path, while offering their mother Pestilence a place at their side.
From there, the Apocalypse Twins prepared the way for their masterpiece. They used a Celestial ship to take down the Peak, the space station headquarters of S.W.O.R.D. that served as an early warning for alien invasion. They also cleaned house by wiping out the Clan Akkaba strongholds, using Uriel's chronomancy to kill thousands of Decimated mutant followers in an instant. In these acts they also left messages for the Avengers Unity Division to drive a wedge between their mutant and non-mutant members. Thor's role in the creation of Jarnbjorn was unveiled, and how Kang used it to cleave the Celestial Armor of Apocalypse and his followers, leaving mutantkind without defenders. They also pulled back the curtain on X-Force, Wolverine's hit squad who had assassinated a child version of Apocalypse and their father Archangel, and that a reckoning was upon him for his actions. Their words had the desired effect, splitting the Unity Division in two, as Thor stood by Logan and the mutant members, while Captain America refused to abandon the moral high ground, keeping Havok and the veteran Avenger members separate from them. [Uncanny Avengers (1st series) #7-9]
The fractured Avengers were vulnerable to capture after that when they pursued the Apocalypse Twins separately. The Horsemen kidnapped Scarlet Witch and Wonder Man for Uriel and Eimin to treatise with. The Twins explained to Wanda that their knowledge of X-Force wasn't merely intended to hurt, but was a harbinger of the days to come. The Avengers Unity Division's first foe had been a clone of the Red Skull with Charles Xavier's telepathic brain. He had temporarily brainwashed Wanda into serving him as he pushed a telepathic race riot onto Manhattan. Uriel and Eimin said that Wolverine's assassination squad was only one of several mutant crimes the Skull had uncovered telepathically, along with Logan's murder of his own son Daken and Akkaba's cleansing of an entire town in Montana. In mere days, his second propaganda strike on mutantkind would reveal these atrocities, leading humanity to accept the mutant concentration camps that Uriel and Eimin grew up in. Wanda would once more fall under the Red Skull's sway, and her vast power would be used to kill Earth's heroes, man and mutant alike, and reinforce his fascist rule.
To prevent this future, Uriel and Eimin offered Wanda a different path: the Rapture. Their Celestial space ark could hold the mutant population of Earth in stasis, long enough for them to reach and terraform a new world into Planet X. Let humanity have Earth if they were so attached to it, while mutantkind built their own paradise elsewhere, without shedding a drop of blood. With the Red Onslaught crisis as a ticking clock, the Apocalypse Twins asked Wanda to willingly cast the Rapture spell, helping them remove the mutant population of Earth before their darkest hour began. Wonder Man, whose ionic body only lived thanks to a previous use of Wanda's power, could act as a living battery to fuel her abilities and make them strong enough to accomplish the Rapture, summoning the mutants and placing them in stasis for the journey. The decision they left in Wanda's hands. [Uncanny Avengers (1st series) #10-12]
While the Twins played with their guests, the Horsemen kept the other approaching Avengers busy. Sentry occupied his murderer Thor as Daken took revenge on his father for murdering him and the Deathseed-twisted Banshee blamed Havok for his brother Vulcan murdering him. All the Unity Division's sins came back to haunt them. Uriel and Eimin visited Wolverine during Daken's torture sessions to brag about Wanda's commitment to their cause and make it clear that everything that happened next was the fault of him and X-Force. Wanda DID agree to perform the Rapture, but she and Simon secretly intended to summon the mutant race to the space ark not in their stasis pods, but as a crusading army of mutants to oppose the Apocalypse Twins.
But it was here that the seeds of mistrust sown by Uriel and Eimin bore fruit. When Rogue and Sunfire learned about the Rapture from the weak and tortured Wolverine, they had no trust in Wanda after the Decimation and the Red Skull riots and thought she had actually switched sides. Rogue attacked Wanda in the middle of her spell, dealing her a lethal blow. Eimin foresaw this as part of their plan, twisting the knife for Wolverine in revenge for his role in killing their father. While Logan had sworn off killing after Daken and X-Force fell apart, Rogue had ultimately learned from his deeds and not his words. He saw Rogue do what she thought he wanted, killing a teammate, before being killed herself by the Grim Reaper. The interrupted spell consumed more of Wonder Man's energies than intended, and he died powering Wanda's Rapture spell, with the Scarlet Witch herself only barely staying alive long enough to finish her work. [Uncanny Avengers (1st series) #13-14]
And it was all for nothing. Eimin misled Wanda that her power was needed to entomb the mutants in stasis. Once the Rapture itself brought all the mutants from Earth to the Ark, the Apocalypse Twins could guide them into their pods regardless of Wanda's intent. The endgame was upon them as mutants from both sides left the field of battle and entered stasis, leaving only Uriel, Eimin and two Horsemen against the founding Avengers Captain America, Wasp and Thor. Captain America reached Uriel and Eimin first, but was unable to defeat them as the true purpose of the Twins' plotting was made manifest: Exitar the Executioner arrived to pass judgment on the Earth for the death of many Celestials. The Apocalypse Twins used Jarnbjorn as provocation to bring about the end of life on Earth. With mutants safely aboard the ark, only humanity would face the Celestials' wrath, and Kang's future kingdom and conquests would be undone as well. [Uncanny Avengers (1st series) #15]
A furious Thor arrived to settle accounts with the Apocalypse Twins, and the astute Captain counseled the Thunder God that separating them would deprive Uriel and Eimin of their time-based powers. Eimin raged at Captain America for her childhood in the Red Skull's death camps, and his failure to stop it. He only managed to evacuate her into space, not defeat her. Meanwhile, Uriel was cocky about his battle with Thor, for Eimin had given him the details of her foresight, and all was still going according to plan. Still, he was surprised by the raw fury of the Thunder God, who had stumbled across the body of his friend and teammate the Scarlet Witch in the melee. Uriel thought to retrieve Jarnbjorn for the final conflict, but was unable to reach the axe before Thor was upon him. Deprived of his weapon and his chronomancy, Uriel fell to Mjolnir's power. To his utter shock, Uriel was pressed through one of the hammer's portals into the heart of a star. The God of Thunder held the Light of the Cosmos in the star's corona, burning away his own arm until Uriel was utterly consumed by the stellar plasma. [Uncanny Avengers (1st series) #16]
As Thor tried to retrieve Jarnbjorn in the devastation that followed, Eimin got to the axe first. She revealed that Uriel's death had always been part of her plan. As much as she loved her twin, her hatred of Kang was stronger, and so she told him what he needed to hear for the plan the proceed. Time ran out, as the Wasp failed to destroy the tachyon dam, even as the Grim Reaper killed Captain America in front of her, because as Eimin predicted she would not compromise her principles against not killing. Eimin kept Thor at bay long enough for Exitar to pass judgment on the Earth, with the tachyon dam ensuring the destruction of the world became a fixed point in the timeline, unchanged and unchangeable. Humanity died, the future empire of Kang died, and Eimin was victorious. [Uncanny Avengers (1st series) #17]
Six years passed, and Planet X was established. With most of the Avengers Unity Division dead or detained, Eimin was able to sell a sanitized version of events to the X-Men and surviving mutants. She claimed her future sight foresaw the destruction of Earth by the Celestials, but told a half-truth that the Space Gods wanted Earth destroyed merely for the creation of Jarnbjorn, leaving out the use she and Uriel made of it. In Eimin's version of events, there was no time to warn mutantkind in advance of the Rapture, which the Scarlet Witch and Uriel gave their lives to accomplish. An X Council was established as ruling body of Planet X, and mutant society thrived there for a time. The only snakes in Eimin's paradise were Havok and Wasp, the sole surviving and free members of the Avengers Unity Division, who still sought to undo what she had done. Havok and Wasp finally destroyed the tachyon dam six years after the annihilation of Earth, but that only allowed time travel into their current era, not further back from the point of the dam's destruction.
Eimin got the X Council to agree to stop Havok and Wasp from interfering any further with their world, with Cable supporting her conclusions that destroying the dam still meant there was no hope for retroactively saving Earth. Secretly, Eimin plotted with Daken to murder the X Council and consolidate her power. She knew the true threat from the tachyon dam falling was a vengeful Kang finding her, and she hoped to both prepare for his arrival and use him as a scapegoat for the Council's deaths as well. Indeed, Kang, his Chronos Corps and a fighting-mad Thor returned to reclaim Jarnbjorn and smash through Eimin's defenses. In a private moment, Kang laughed at his adopted daughter's perceived successes, and gloated that her treachery was merely a planned facet of his own overarching schemes. Wolverine and Sunfire were rescued from Eimin's clutches, and the remains of the Unity Division proceeded with Kang's plan to save the Earth. [Uncanny Avengers (1st series) #18-20]
With the help of his Chronos Corps allies Doom 2099 and Magistrate Braddock, Kang beat the tachyon dam by transmitting the minds and memories of the surviving Avengers Unity Division back in time instead of physically traveling there. The Avengers prevented Wanda's Rapture spell and the deaths of her and their fellow heroes. Unaware of their previous success, Uriel and Eimin only saw the carefully choreographed steps of their plan falling apart. Eimin's foresight was still blocked by the tachyon dam in this era, and so she could not chart these changes in the timeline either. When Exitar arrived, Thor already had Jarnbjorn and used the axe to slit the Executioner's throat, killing the Celestial before it could destroy Earth.
This moment was the final culmination of Kang's lifelong plans for the Apocalypse Twins. The Conqueror's cruel treatment of Uriel and Eimin was intended to sow dissent and rebellion in the twins. In his lessons, he deliberately seeded the idea of destroying the Earth of the past in Eimin's mind, leading her to believe it was her plan and would obliterate Kang's own empire. In truth, it did temporarily, but the threat allowed Kang to gather the powerful Chronos Corps from several future timelines which were being annihilated. The Corps were bound to obey Kang, for only he had a plan to restore their lost timelines by undoing the Apocalypse Twins' work. And when Thor killed Exitar after the Unity Division brought down the tachyon dam in the present, Kang was there with his Conqueror's armor primed to absorb the Celestial energies and grant him the power of a god.
Despite all their scheming and plotting, the Apocalypse Twins were reduced to bit players in the finale of Kang's magnum opus, virtually forgotten as Earth rallied to defeat the all-powerful Kang and his Chronos Corps allies. With the tachyon dam down, Eimin returned to her piano and foresaw their coming end. Uriel never learned his sister planned to sacrifice him to achieve their goals. The space ark was shot down in the final battle with Kang, sending the Twins to the planet below. Kang was defeated in their absence, the Rapture was prevented and even the Red Onslaught was ultimately undone. Uriel and Eimin were last seen, battered and bruised, being removed from their fallen ark by their remaining Horsemen. Whether or not they survived, the life's work of the Apocalypse Twins was a failure, for their hated foe Kang had outplayed them before they were even born. [Uncanny Avengers (1st series) #21-22]