The story of the Kryptonian Worldkiller Reign from Season 3 of the TV series Supergirl.
The Kryptonian Worldkiller known as Reign was born on the dying planet Krypton. Alongside the other Worldkillers, her own physiology was genetically modified at birth which would allow her to not require solar energy for her own powers, and also be able to shrug off possibly all types of Kryptonite. On the day of Krypton's destruction, as a baby, she was placed inside a pod and sent to Earth to grow up and begin her path of "cleansing" and to "preserve the awakening", alongside the other Worldkillers. When arriving on Earth, she was found in her pod by the human Patricia Arias, who then adopted her as her own daughter and gave her the name "Samantha Arias". At some point prior to turning 18 years old, Samantha got pregnant to an unknown man, and was therefore kicked out by her own adoptive mother which left them estranged. This forced Samantha to raise her daughter, Ruby, as a single mother, balancing her work and ensure a comfortable future for them both. Unknown to Samantha though, her pregnancy to Ruby delayed her manifestation into becoming 'Reign'. At some point in her life, she got a job at L-Corp.
12 years later in late 2017, Reign was unexpectedly triggered when Samantha used super strength to save Ruby's life. Reign's powers began to emerge, cumulating in her transforming into a hideous monster in Juru. The transformation was presented to Samantha as a "nightmare", a warning of the Worldkillers' "End of Days" prophecy coming into fruition.
As the weeks passed, Reign's powers began to grow stronger, affecting Samantha and soon rendering her skin invulnerable.
Upon discovering her powers, Samantha was prompted to seek out the truth of her past from Patricia. Patricia showed her Reign's pod, from which Samantha uncovered a crystal. In a remote desert, the crystal uncovered the Fortress of Sanctuary, a piece of Krypton which would house and advise the Worldkillers. The fortress' hologram of Selena, the leader of the Children of Juru, preached that it was time for Reign to emerge. Despite Samantha's resistance, Reign began to completely manifest in her host, painfully repressing Samantha's human self. Her eyes glowing red, Reign eerily stated, "I have awoken" in ancient Kryptonese.
Upon the behest of Selena's hologram, Reign aimed to prepare Earth for the "End of Days" prophecy and returned to National City to make her mark. Using her heat vision, she burned the Children of Juru's symbol all over the city throughout the night, completing the first step, the "Mark of the Beast".
A couple of nights later, Samantha saw a news report from L-Corp about a street gang known as the One-Seven Gang causing yet another fatal shooting. Reign was angered by this and began to emerge, but Ruby's arrival at the office brought Sam back to the surface. After Ruby left, Reign took control and flew to the National City Port, where she caught the One-Seven Gang participating in a drug deal. Reign attacked the gang, swiftly and brutally ripping its members to death with her heat vision as punishment for their criminal actions.
Later that night at CatCo Worldwide Media, Samantha learned of Morgan Edge's assassination attempt on her friend and boss, Lena Luthor. She angrily gazed at a picture of Edge and with Reign awakening, coldly stated that he should be dead. Reign exited, ripping open her buttoned blouse to reveal her suit with the Children of Juru's sigil upon her chest. Reign attacked Edge Global during a Christmas Party that night, inciting havoc in the building. She made her way to Edge's office, but he concealed himself in a lead-lined panic room. Unable to spot him through the material, Reign wordlessly left by flying out the window.
Supergirl, intending to draw this new and mysterious Kryptonian out, left her symbol of the House of El on the roof of CatCo. Sensing the challenge, Reign arrived on the roof and waited for the superheroine to arrive. Once Supergirl and Reign met face to face, the former wondered if her opponent was the Devil. Reign negated this, introducing herself as a dispenser of justice on Earth. The Worldkiller revealed she too is from Krypton, having been sent away right before the planet's collapse. Supergirl condemned Reign's terrorizing of the city, to which the Worldkiller protested that the world had been broken down by sin and she will ensure that judgment was dealt to those who eluded it. Supergirl refused to allow her crusade and demanded that the Dark Kryptonian surrender, or else. Amused by her opponent's hubris, Reign compared Supergirl to the residents of Krypton, who worshipped "false gods" while fearing and shunning her creators. Reign claimed the modern Kryptonians let their planet suffocate and burn, threatening to send Supergirl to Purgatory with them if the superheroine tried to get in her way. When Supergirl refused, Reign decided to dispense her justice on her and the two engaged in a fierce duel.
Reign and Supergirl's battle raged throughout National City, leaving a trail of destruction, with the two superbeings evenly matched at first. They soon crashed onto the streets, dueling in front of hundreds of civilians. Reign eventually managed to knock Supergirl down with a punch to the face. As Supergirl became distracted by some nearby onlookers, Reign struck her head with a slab of concrete, drawing blood from the Girl of Steel. As the disbelieved and slightly concussed Supergirl attempted to continue fighting, Reign quickly incapacitated her with a head-butt. Supergirl gathered enough strength to disarm Reign of the concrete and use it to push her away, but the Worldkiller quickly flew back into proximity and hurled a flaming car door at Supergirl before using her heat vision to burn off the Girl of Steel's crest and force the latter onto a roof. Picking up Supergirl by her suit and musing that her weakened and beaten down opponent wasn't a God, the Worldkiller proclaimed she wasn't the Devil, but an entity of truth, justice, and death who would reign. She then dropped Supergirl from the roof, watching as the Girl of Steel fell to the ground and seemingly died. After her triumph, Reign presumably returned to Samantha's home.
Fighting the Legion
Two days later, Reign took over Samantha upon seeing a newspaper reporting her defeat of Supergirl. She returned to the Fortress of Sanctuary, where Selena's hologram congratulated the Worldkiller on her victory over Supergirl and making her mark. Reign was quickly informed that was still much for her left to do in preparation for the awakening that she is meant to enact. The hologram ordered her to exact deliverance on Earth and target not just sinners, but those who allowed sins to happen through their inaction. Reign then murdered a thief who stole a van and broke into CatCo, where she dropped off the man's body. Reign ordered one of the nearby cameramen to aim his device at her and, despite Lena's protests, began broadcasting her message. Reign accused the people of National City of allowing criminality to roam free in city, as well as being apathetic towards the plague. The Worldkiller declared that she is "here to help" and vowed to show no mercy against such people before flying away.
True to her word, Reign began to target criminality in all its forms, as well as the city's justice system if she deemed they didn't punish criminals enough; she took down a meth lab and then the police when they arrived to stop her.
Later, Reign descended on what appeared to be a bank robbery, preparing to kill the perpetrators. However, the "robbers" and some "hostages" were revealed to be agents from the D.E.O., having set up the operation to lure out the Dark Kryptonian. Initiating the Sundown Protocol against the Worldkiller, the agents attacked Reign with a red sun grenade and sonic weapons, disorienting her. Two agents then pinned her down with a heavy metal wire while Alex Danvers placed a chain of Kryptonite soil around her neck. Reign was initially weakened and in pain, but overcame the Kryptonite's effects and broke her restraints. She used the metal wire to snap Alex's tibia in half, knocking her down. Furiously casting the Kryptonite aside, Reign attempted to kill Alex, only for J'onn J'onzz to intervene and punch her aside. Reign then escaped through a window.
In retaliation for the ambush, Reign invaded Albatross Bay and went on a rampage, striking down convicts and guards alike. She eventually came upon a holding cell and found Thomas Coville praying to a Juru glyph, submitting to her will. Intrigued, Reign wondered how Coville knew those words, to which he preached to be "awoken to them". Reign suspiciously asked if Coville believed claiming salvation would result in her sparing him but Coville revealed he in fact wished to be of service to the Worldkiller's cause. Just then, Reign heard Bon Jovi's "Livin' on a Prayer" blaring outside and left to investigate. Busting through the prison wall, she was faced with a large spaceship rising out of the water with Mon-El and Imra Ardeen preparing to duel her.
Reign warned them not to interfere, as she wanted to purge the world of sin. Imra rhetorically asked why she doesn't start with herself, to which the Worldkiller retorted that she's "not of this world". She flew to the spaceship but the two Legion members to followed her. The ship attempted to shoot Reign down, but she ended up redirecting one of their missiles back to the cannons, destroying them. Imra telepathically threw some weights at Reign while Mon-El rushed at her with a Kryptonite syringe. However, Reign destroyed the weights with her heat vision and used her freeze breath on Mon-El, though Imra saved him with a telepathic bubble. J'onn then ambushed Reign, phasing the both of them underground. After a brief battle, the two flew back above ground, both injured, with their match having ended in a stalemate. When Imra tried to free Mon-El, Reign knocked her aside and prepared to kill Imra for protecting a "sinner". Just then, Supergirl arrived, much to Reign's shock, having believed the Girl of Steel to be dead by her hand. Supergirl attacked the Worldkiller and they both tumbled onto the ground. Reign tried to finish off the superheroine, only for Supergirl to plunge a syringe of concentrated Kryptonite into her neck. Stumbling and gasping in pain, Reign quickly fled.
Reign managed to make her way back to the Fortress of Sanctuary. Writhing in agony until the Kryptonite was flushed out of her bloodstream, Reign soon recovered and was questioned by Selena's hologram as to what happened. The Worldkiller admitted Supergirl gained an edge on her due to unexpected allies. The hologram then revealed to Reign the existence of other Worldkillers, whom she could find on Earth now that she had proven herself. Coville then arrived at the Fortress of Sanctuary, offering to help Reign complete her path.
Searching for the Others
A week later, the Fortress of Sanctuary sent out Kryptonian phrases that only Reign alone could hear, causing her to emerge and fly there. When Selena's hologram wondered why she arrived late, the Worldkiller expressed that her human side is stronger than she expected; Samantha's increasing resistance, while subconscious for now, made it increasingly difficult for Reign to take and maintain control. The hologram scolded that Sam shouldn't be a hindrance and informed her that the Fortress had detected a signal coming from Fort Rozz. The hologram explained that Supergirl and her allies were headed to the prison, most likely to find Jindah Kol Rozz, the dark high priestess of the Children of Juru who had been imprisoned long before Krypton's destruction. Realizing that Supergirl gaining any of Jindah's knowledge of the Worldkillers' agenda would pose a threat to their plans, Reign boarded her pod to Fort Rozz, intending to find the priestess first.
At Fort Rozz's Dendara Corridor Reign, Reign witnessed Jindah revealing to Supergirl the existence of Purity and Pestilence, the other Worldkillers who would unite under their leader, before announcing her presence and greeting the priestess. Jindah expressed delight to see Reign, believing the two will unite to bring hellfire upon their enemies and restore the Juru's way of life. However, Reign instead deemed Jindah to be a liability and fired her heat vision through the priestess' heart, killing her. Supergirl was shocked that Reign's powers weren't dampened by the blue star Fort Rozz was orbiting, to which Worldkiller gloated that the sun isn't the source of her strength.
Reign mocked that Supergirl was vulnerable whilst de-powered but the superheroine nonetheless tried to reason with Reign; she expressed her belief that a part of the Dark Kryptonian regrets the pain and terror she is causing in her mission (unknowingly reaching out to Samantha), insisting they could deliver justice the right way without being at odds with one another. Reign disagreed and prepared to kill her, only to be attacked by Supergirl's ally, Leslie Willis/Livewire. Livewire battled the Worldkiller, with Reign unable to get a direct hit on the meta-human at first due to her electricity-phasing powers. Once Livewire manifested, Reign derided her as a "nuisance" and fired her heat vision, which the former countered with her electricity. The two powers were evenly matched until Reign got close enough to begin choking Livewire. Supergirl tried to intervene, but was knocked aside. A furious Livewire ordered Reign to leave her friends alone before summoning enough electricity to push each of them back.
Though winded from the encounter, Reign recovered in seconds and descended on an incapacitated Livewire, enraged. Supergirl pleaded her to spare Livewire and offered herself instead. Reign agreed and fired her heat vision at Supergirl, only for Livewire to take the hit, mortally wounding her. Just then, Gayle Marsh/Psi, another one of Supergirl's allies, confronted Reign. As the Worldkiller studied her foe, Psi unleashed a psychic attack on Reign to tap into her deepest fears. Reign immediately began crying out in pain and distress, with Psi's crippling energy overriding her powers and forcing Samantha to the surface by exposing her worst fear - Ruby being taken away from her forever. Once Samantha recovered from the ordeal, she was scared and confused about her current situation but before Supergirl and her allies could help her, Reign took back control of her human host and fled from Fort Rozz, returning to Earth.
Several weeks later, Reign was summoned to the Fortress, where the hologram revealed that one of her sisters, Purity, is beginning to awaken due to the latter's crystal activating but had already been discovered by their adversaries. The hologram urged Reign to retrieve her sister, who needed be brought to the Fortress for their guidance to ensure the Worldkillers' success. Reign agreed and set out to search for Purity.
Reign eventually tracked Purity to the subway, where she met her sister's human half, Julia Freeman. With Supergirl and Mon-El incapacitated earlier by Purity and J'onn occupied with holding up the collapsing structure, Reign immediately moved in. Alex fired her alien gun at the Worldkiller, but Reign quickly disarmed and knocked her down before beginning to crush Alex's ribs with her foot. However, Julia freely gave Reign the opportunity to take her in exchange for sparing Alex. Sensing Purity within her, Reign agreed. Now one step closer to their plan, Reign mused how the Worldkillers would ascend once united. Before the heroes could intervene, Reign abducted Julia and brought her to the Fortress.
Later that night at L-Corp, Samantha's increasing worry and stress with how her latest blackout nearly put Ruby in harm's way, combined with anger when she believed Lena revealed the former's episodes to her daughter, began to trigger the Worldkiller. Amidst Lena's attempts to talk to Samantha, Reign emerged and menacingly yelled "Silence!" before threateningly advancing on her. However, when Lena called out her friend's name, Samantha immediately woke up from her trance and suppressed Reign
Learning the Truth
A few days later, Lena deliberately angered Samantha to awaken Reign, needing proof of the Worldkiller's existence. Reign tried in vain to escape from the laboratory before Lena suppressed her with a dose of synthesized Kryptonite, though not before obtaining a sample of the former's DNA.
In an effort to isolate and override the enzyme which triggered Reign's manifestation, Lena used electric shocks to stimulate Samantha's pain receptors in order to gain access to the Worldkiller's genome while still suppressing her subconsciousness. As Reign awakened, she met her human self in person for the first time in Juru and cryptically warned Samantha that the Worldkillers were coming for them. Just then, Samantha awakened and took back control.
Not long after, Reign encountered Samantha again in Juru. Admitting her human half was stronger than she thought, the Dark Kryptonian vowed to change that, vengeful about being locked in Juru alone for so long. Reign tried to tempt Samantha into giving into the darkness, promising it was a way to escape the isolated existence she had been "trapped" in since her daughter, Ruby, was born for one of power and control. Reign offered Sam the opportunity to unite into one being, but was refused and suppressed once more.
Reign confronted Samantha in Juru one last time, reiterating her offer. However, Sam rebuffed her again, determined to ensure the Worldkiller would never escape the dark valley. Angered at the rejection, the Dark Kryptonian grabbed Sam by the throat and began choking her, deciding to force her human half to submit instead. Reign vowed to completely annihilate Sam's home and burn it to ash, sadistically promising to personally "cut [Ruby] inside out", taking away her human half's source of strength. Sam resisted and eventually awoke.
As Reign sensed the impending arrival of Purity and Pestilence, she became strong enough to begin dominating over Samantha, forcing her alternate self into Juru. When Supergirl, J'onn, Mon-El, and Imra arrived to warn Lena, the Girl of Steel was shocked to see Reign, recognizing her civilian identity. Reign stated her sisters were coming before Lena gave her another dose of Kryptonite. Just then, Purity and Pestilence arrived and destroyed the laboratory protocols, releasing Reign. Elated to finally join her sisters, Reign transformed into her costume and chanted "El mayarah". The Worldkiller trinity unleashed a powerful wave of crippling energy onto the heroes before escaping.
Returning to their fortress, the three formed a trinity in their attempt to destroy their human personas, in which they were successful in Grace's. However, before they could destroy Sam and Julia's, Supergirl and the others arrived and intervened. As Julia regained control, both she and Pestilence killed each other, resulting in their energy binding to Reign and granting her their powers as she escaped. Knowing that the human side of hers needs to die, she sets out to kill Sam's daughter Ruby.
Captured and Separated
Through an endless search, Reign was able to find Ruby at Lex's mansion, stored there by Lena. During a fight with Mon-El and Supergirl, her mask knocks off, revealing herself to a horrified Ruby. After Supergirl reminds Reign of her code to only kill the sinful, they are able to overpower and capture her before she could do more harm. Being kept at Lena's lab while Supergirl and Mon-El go off to find the Harun-El rock that could save Sam, Reign taunts Lena about how she had darkness inside of her, just like her. After she breaks out, Supergirl and Mon-El arrive and inject her with the Harun-El, mix with a sample of her blood extracted by Lena. As a result, Reign was finally separated from Sam and became her own person while still connected to Sam's life force. Later on, Reign was resurrected by the Worldkiller priestesses in their bid to complete their mission: to make Earth their new homeworld and destroy the human race.
Final Battle and Death
After being resurrected, Reign is sent to terraform the Earth in order to make it their new Krypton. However, she, along with Selena and the other priestesses, were confronted by Supergirl and the others. Reign, however, still proved too powerful for them. As she ranted how no one was powerful enough to defeat her and that there was no prison that could hold her, Samantha used the Sword of Juru to stab her and wound her, angering the Worldkiller enough to attack her. Reign was killed by Sam, who put the water from the Fountain of Lillith into to her mouth, causing wraiths to surround Reign and fly her into the Fountain of Lillith.