Halo Alpha
Halo Alpha

Kai-125 was a brand-new, courageous, curious and deadly Spartan super soldier.


Kai was conscripted into the Spartan program by UNSC scientist Catherine Halsey, having been kidnapped from her home under the age of five. Designated as "125", she was subjected to genetic and physiological enhancements that pushed her intelligence, physical ability, stamina, and endurance far beyond what a normal human body was capable of.

She also underwent procedures that eradicated all memories of her childhood, while conditioning her to be absolutely loyal, unhesitant in carrying out orders, and averse to dissent or noncompliance. Kai was programmed to believe that she had joined the UNSC of her own free will and volunteered to become a Spartan. She primarily trained alongside John-117, Soren-066, Vannak-134, and Riz-028.[1]

Battle on Madrigal[]

Kai assisted the Silver Team of Spartans in a mission on the planet Madrigal, where a squad of Covenant Elites were attacking. After defeating the alien creatures, Master Chief and his team examined the perimeter for signs of any other Covenant forces. Kai and Master Chief discovered a man-made cave in which the Covenant were excavating an artifact. When Master Chief interacted with the object, the cave came to life with energy. Kai pulled him off and they chased a lone surviving Elite who escaped the planet. Kai wanted to accompany Master Chief to Reach, but he ordered her to act against protocol by returning with the other Spartans so he could travel alone - later going AWOL, leading Admiral Parangosky to initiate a kill order. Dr. Halsey overrode this order with one of her own - protect Master Chief at all costs. Riz questioned if this means firing upon friendlies, though Vannak iterates that if they are firing on Master Chief then they aren't friendlies. The trio heads to the landing bay, but their expertise is unneeded as Master Chief escapes the assault and flees Reach.[2]

Halo 102 Kai-Vannak-Still

In the days that follow, Kai talks to Vannak about Master Chief going AWOL. She learns that he still hasn't turned on his beacon. They are tasked with tracking Master Chief and take flight to follow his movements. They remark on his odd movements such as jumping through an asteroid field. Kai wonders why he's doing this, but Riz and Vannak don't seem to question it. The next day, Master Chief activates his beacon and allows Silver Team to apprehend him and return him to FLEETCOM.[3] John returns to Spartan Headquarters when Cortana appears to introduce herself to the team. John snaps that he didn't summon her and tries to dismiss her, but she only questions his vernacular before politely excusing herself. John remarks that the new A.I. is not permanent. As Chief settles in, Kai secretly watches him remove his hormone pellet with help from Cortana.[4]

Pellet Removal[]

Halo 104 Kai-Still3

Inspired by Master Chief's removal of his hormone pellet, Kai takes action to remove hers by herself. After successfully doing so, she begins to exhibit small bursts of rebellion and curiosity as she explores the world around her. She impulsively dyes her hair using grease. When Dr. Keyes recruits the Spartans to run tests on the Madrigal object, Kai is the only Spartan to talk back to Miranda and touch the artifact prematurely. She doesn't appreciate the dismissal of the Spartans attributes and even lists which each of them brings to the table.

While performing more tests in her lab, Miranda admits that she thought her mother kept her from the Spartans because they were more fun, but now she doesn't believe fun was part of their training. Kai corrects that they did have fun, as they each had pets growing up and would play hunter and hunted in the woods. The loser had to eliminate their pet, with Kai pausing as she remembers her cat. Vannak-134 never lost a match, though Halsey executed his pet to teach them that Spartans should only form attachments to one another. Miranda is mortified at Halsey's display of apathy, but the story doesn't affect Kai, Vannak, or Riz-028, who see it as a normal aspect of life. Kai excitedly picks up a Needler, a Covenant weapon, and reveals Riz's knowledge of the Sangheili language. In fact, the Spartans have spent the most time with the Covenant and know much of their language, something Miranda is remiss over not realizing sooner.

Halo 104 Kai-Miranda-Still

Once alone, Miranda sits with Kai to review the distress call sent from the hijacked UNSC ship. Kai translates one word as "keystone", another as "sacred ring", and notices the ring that appears around the Madrigal keystone. She and Miranda realize that the sacred ring is the ring projected from the Madrigal artifact. Miranda asks Kai to keep their discoveries a secret, and Kai obliges, though she asks for Miranda's honest opinion on her grease-dyed hair. Miranda thinks she dyed it out of rebellion, which might be a glitch in her programming. Nonetheless, she warns that Halsey doesn't cope well when her creations don't act as designed.[5]

Halo 105 Kai-Vannak-Still

The Spartans are reassigned to provide support in the extraction of the second artifact on Eridanus II. Kai continues to barrage Vannak with what he calls "dumbass questions" over his beliefs about orders and why things are the way they are. Her new hair color catches the attention of both Master Chief and Cortana, who have vastly different opinions. Master Chief questions when Kai removed her pellet, which was the day after he removed his. She knows why he did it too. The world is brighter and clearer with her emotions brimming with excitement and curiosity. Master Chief sidelines her from the event as he can't trust that she'll perform well in battle. She questions that if she's such a liability, what he is, then. She follows orders and stays with Miranda until the Covenant attack Eridanus.

Halo 105 Kai-Still1

Miranda commands Kai to join the fight and she leaps into action with her fellow Spartans. Their orders are clear - protect the artifact and get it to Miranda. Kai is told to cover the Spartans and marines with sniping, which she does excellently. As she joins the ground battle she witnesses the marines dying, being brutally murdered, viewing the bloodshed and mayhem around her. She becomes overwhelmed and the Covenant take advantage of this vulnerability and attack her relentlessly. She falls to the ground as her armor struggles to protect her from the barrage of attacks. Master Chief spots Kai on the ground and abandons his post as he can't let her die. He succeeds in saving Kai from the aliens, but inadvertently causes the Warthog with Vannak, Riz, and the artifact inside it, to crash. The Covenant steal the artifact and escape, leaving only a human prisoner in their wake.[6]

The survivors of the battle return to Reach. Kai's injuries have her screaming in agony as the injections aren't quelling her pain. Master Chief sits next to her as he holds her hand, obliging to Vannak's request to keep her still while Riz injects more medicine. Finally, Kai goes unconscious and medics tend to her wounds. She recovers slowly as mobility in her arm remains limited even after her procedures. John visits her to tell her about his discoveries. He learns that all the Spartans were kidnapped as children by Halsey for the Spartan program. Their bodies were swapped with genetically flawed flash clones so their parents could, eventually, grieve the death of their child. Kai is mortified at the reveal as her whole life has been a lie. She wonders if her parents are still alive, but all the files pertaining to the creation of the Spartan program were lost. John will tell the other Spartans when they are ready, but not until then. He wants Kai to get better as he'll need her for what's coming. She agrees to keep quiet until he's ready. When she regains some of her strength and visits Riz and Vannak who are discussing their new weapons upgrades. Kai struggles to keep quiet about her knowledge but does so anyway.[1]

Fight for the Halo[]

Kai spends the rest of her time recovering from her wounds by pushing her body its limits. She showcases her inhuman strength by dragging a metal pipe with only a rope, lifting a warthog into the air with several passengers while onlookers cheer, and goading people to test her abilities with a real challenge. She enjoys some down time when Halsey, through Cortana, alerts the Spartans that Zed Protocol is now active. Under the protocol, all senior officials - including Master Chief - are considered compromised, which Halsey laments is because of the Madrigal artifact. John is especially compromised because of his prolonged exposure to its affects. As such, the Spartans suit up in their FLEETCOM base.

Halo 108 Kai-Still

Halsey orders Silver Team to bring John, Makee, and the artifact to her ship where they will all leave Reach together. Kai inadvertently alerts Halsey after a hormonal fluctuation is detected - the result of her pellet removal. She thinks there is another way to help John, insisting that he's their friend and they can't just abduct him, let alone fight him. Halsey cuts off communication to and from Kai, then tells the other Spartans that Kai has been compromised too. Subsequently, Riz and Vannak knock Kai unconscious and tie her up in the showering quarters.

Halo 108 Kai-Still2

When Kai wakes up, she tries to free herself from the cuffs, which are attached to a countertop. She swings her legs behind her head and uses her strength, force, and armor to break the countertop. She repeats this motion several times until she can free her hands and procure her helmet. She rushes out of the showering quarters and past a marine, who she to ensure Halsey's ship doesn't leave the tarmac, giving them permission to shoot it down if they need to.

Halo 108 Vannak-Kai-Still

Kai rushes across FLEETCOM to where John, Riz, and Vannak are engaged in an intense fight. Kai leaps into action to help John, though the foursome reach a stalemate; Riz has her gun on John, while Kai and Vannak have drawn on each other. John and Kai try to get through to their teammates but their orders have changed to bring John in - dead or alive. Suddenly, an energy blasts through FLEETCOM as Makee makes contact with the Madrigal artifact across the base. It blasts the Spartans to the ground and away from one another.[7]

As the effects of the Halo's blast wears off, Kai is taken hostage by Riz and Vannak. They find John and leverage Kai for him to come with them. John, not seeing any other option, reveals that Halsey kidnapped them as children and stole them from their parents. She forced them to become Spartans. Kai reveals that she knows and he's telling the truth. Riz wavers in her belief but Vannak doesn't, pointing a gun to John's head. Miranda and Jacob arrive in the midst of the conversation, but hear John trying to reason with the Spartans by telling them the truth of Halsey's horrendous actions. They don't believe him until Jacob admits to being privy to the activities and helping to plan their kidnappings. This is enough to break through to Riz and Vannak. Silver Team splits up, with John, Riz, and Vannak head to the ship bay to stop Makee from escaping, while Kai goes after Halsey alone.

Military troops are ordered to shoot down Halsey's ship to keep it from leaving the tarmac. As the ship prepares for flight, the troops open fire, but it isn't enough to subdue the ship. Kai, infuriated at the idea of Halsey escaping, runs at inhuman speeds, leaps into the air, lands on Halsey's ship, and proceeds to shoot the engine with her gun. She then breaches the cockpit. Adun tries to close the door to block Kai from entering, but she grabs the closing doors and pries them open with a shout. She removes her helmet and turns to Halsey, demanding to know her real name.

Halo 109 Kai-Still

Halsey assures her that her name is Kai-125, but the Spartan wants to know the name her parents gave her. She wants to know who she is - Halsey admits she's exactly who she was meant to be. Adun strikes Kai over the head, which only angers her. She grabs Adun by the throat and slams him through the ceiling, killing him. Halsey flees into an escape pod while Kai bangs on the door separating them. Halsey escapes, leaving Kai in the failing ship that is falling through space. the ship crashes into the landing zones and erupts into flames. Silver Team watches the plan burn, and moments later, Kai remerges.

Silver Team heads on a dangerous mission to find the Covenant's holy planet of High Charity. She boards the plane with Riz and Vannak, asking if they really would shoot her, though they immediately agree. Vannak knows she would have done the same, but Kai at least would have felt bad about it afterwards. The trip there is rocky as they are almost "spaghettified" by the atmosphere surrounding High Charity. As they advance their cover is eventually blown, triggering thousands of Covenant forces to emerge from the grounds to attack them.

An intense battle ensues as Silver Team is quickly overwhelmed. John sees Makee from afar, but faces an onslaught of attacks from the best of the Covenant. Makee makes contact with the now-assembled keystones to save John from the ambush. She succeeds as the blast knocks the Covenant to the ground and they proceed to kneel to watch the event unfold. When she touches the artifact both she and John are rendered unconscious and taken to the Halo.

Halo 109 Kai-Still2

Kai struggles to keep the Covenant at bay while protecting a badly wounded Riz. Vannak takes position at the top of the temple, firing on the aliens below. He remarks their need for the Chief to be online, with Kai unable to reach through to the Chief by shouting at him. Vannak is incapacitated by a group of Covenant. Kai, seeing no other option to free the Chief, fatally shoots Makee. With Makee dead, the star map to the Halo is incomplete. One of the aliens places a plasma grenade on Riz, but when Kai goes to help, they are both caught in the detonation.

The Covenant shifts their focus to killing the Spartans and capturing John, quickly overwhelming the already weakened Spartans. Master Chief is forced to make a choice - save the Spartans or steal the keystone. He surrenders his body to Cortana as she can save both the team and the keystone. She is reluctant she isn't sure she can pull him back or repair his psyche once she resumes control. He relents that he trusts her and gives himself over to the Covenant to attack, which forces Cortana's hand. She assumes control over him and demolishes the Covenant forces.

Master Chief carries the artifact and leads the Spartans aboard their ship where they take-off into the sky, having won this battle. Riz is severely injured so Master Chief silently cauterizes her wound before assuming control over the ship as the pilot. Kai joins him and reluctantly asks John if he's in there. Master Chief silently stares out into space.[8]


UNSC specialists are able to sever the connection between Master Chief and Cortana, though his actions leave Silver Team sidelined from all combat missions. They are asked to assist during a civilian evacuation on the planet Sanctuary. Kai and Vannak discuss his pellet removal moments before the planet is attacked by Covenant forces. Silver Team tries their best to save the residents of the planet, though most of them refuse to abandon their home. Kai and the Spartans witness the planet being glassed by the Covenant as they evacuate. Once back at FLEETCOM, Kai Kai speaks with Riz, where she suggests Riz take time to heal. Despite Riz's insistence that she is ready for battle, Kai expresses concern for her colleague's well-being.[9]

Kai speaks to John (Master Chief) about the presence of Makee on Sanctuary. Despite John's assertion that he saw Makee, Kai informs him that Makee is deceased. Later on, Kai is pressed by Ackerson for information about John, with Ackerson expressing worries about potential risks to the team. Kai reassures Ackerson that John is fine.

Halo 203 Kai-Master Chief-Still

John calls his team to go on a mission to Visegrad Relay. Kai straps in and asks him what the mission is.[10] The team flies to Visegrad where they encounter similar recordings to the ones Master Chief heard on Sanctuary. Before they can investigate the base further, UNSC operatives arrive to arrest the Spartans for an unsanctioned mission. Kai and the rest of Silver Team are willing to disobey the operatives to follow Master Chief, but surrender when the room he's convinced houses proof that the Covenant are on Reach is empty. The unsanctioned mission puts Silver Team in a position of disobedience with Keyes and the ONI. John argues his position as he knows that Cobalt Team were on Visegrad, though Keyes shows a different flight plan than the one John found earlier. Keyes relieves John-117 from active duty and confines him to barracks until he clears a psychiatric evaluation. He will submit to neurochemical and behavioral monitoring. John's team is upset that he lied to them and disobeys his orders to listen to his story. Kai tells John that he's out of control and erratic. She's questioning his judgment ever since he's been seeing dead people. She didn't tell anyone what happened and is trying to help him. He doesn't need her as a friend but as a Spartan.

Kai is called into a meeting with Ackerson where she admits that she, Riz, and Vannak were in the dark about the mission not being authorized. She understands Master Chief needs discipline after going outside the chain. But the Spartans aren't built to sit around and wait. He won't change his decision. She requests to be deployed by herself until John's cleared. Ackerson reveals that John escaped the facility. She doesn't know anything about what he's planning. He's reviewed the file and thinks John may have been changed before Cortana. People don't always get better. Kai can't stay and watch it happen.[11]

The Fall of Reach[]

Covenant forces who are residing on Reach, just as Master Chief believed, attack the planet.[11] While Reach falls to the Covenant onslaught, Kai is across the galaxy in Camp Currahee, where she leads thousands of marines who are ready to continue the fight.[12]

Battle for the Halo[]

Kai led a team of Spartan IIIs to on a suicide mission to attack a Covenant ship. Just as it appears they will be wiped out, John appears and they are able to take control of the ship. Kai deviates for her original mission and decides to ram the ship into the lead Covenant ship, which is thought to have killed her. However later she is seen to be drifting in space, leaving her fate uncertain.


With the pellet that restricts her emotional capacity and ranges, Kai is rigid, disciplined, obedient to her programmers, and deeply loyal to her teammates. She has a strong connection to Master Chief, ensuring his safety above all else, which is a byproduct of her programming to follow orders and respect her superiors. Even with her emotions dulled, Kai is extremely curious and observant, noticing Master Chief's behavior variations when no one else does. Her curiosity led her to remove her pellet, which opens up a world of emotions to her. She shows a streak of rebellion when she dyes her hair, vocalizes her emotions for the first time, and experiences bursts of raw excitement that contrasts her teammates stoic nature. Her emotions level out after six months without her pellet. She can experience compassion, empathy, and concern without the contrasting euphoric emotions that were previously present. Kai remains loyal to her teammates and obedient to Master Chief. She doesn't voice concerns over his orders - even when she has them.

Behind the scenes[]

While Kai is an original character created solely for the television series, she shares a forename with Kai-A019, a SPARTAN-III commando with the UNSC Navy. Her name is also shared with a Covenant vehicle in the video game, Kai-pattern strikecraft.