Kai-125 is a brand-new, courageous, curious and deadly Spartan super soldier.
Battle on Madrigal
Kai assists and the Silver Team of Spartans in a mission on the planet Madrigal, where a team of Covenant Elite are attacking. After defeating the alien creatures, Master Chief and his team examine the perimeter for signs of the Elite ship. Kai and Master Chief discover a man-made cave in which the Covenant were excavating an artifact. When Master Chief interacts with the object, the cave comes to life with energy. Kai pulls him off and they chase a lone Elite who escapes the planet. Kai wants to accompany Master Chief to Reach, but he orders her to act against protocol by returning with the other Spartans so he can travel alone. He goes AWOL, leading Admiral Parangosky to initiate a kill order. Dr. Halsey overrides this order with one of her own - protect Master Chief at all costs. Riz questions if this means firing upon friendlies, though Vannak iterates that if they are firing on Master Chief they aren't friendlies. The trio heads to the landing bay, but their expertise are unneeded as Master Chief escapes the assault and flees Reach.
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. 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.
Inspired by Master Chief's removal of his hormone pellet, Kai takes action to remove hers alone. 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 or the Spartans attributes and 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. Kai excitedly picks up a Needler, a Covenant weapon, and reveals Riz's knowledge of the Shangeheli 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.
Once alone, Miranda sits with Kai to review the distress call sent from the hijacked UNSC ship. Kai translates one of the words 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, but warns that Halsey doesn't cope well when her creations act out of the normative.
The Spartans are reassigned to provide support in the extraction of the second artifact. Kai continues to barrage Vannak with what he calls "dumbass questions" over his beliefs of orders or 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 that makes him. She follows orders and stays with Miranda until the Covenant attack Eridanus.
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, 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.
The survivors of the battle return to Reach. Kai's injuries have her screaming in agony as the pain 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 her bleeding wounds are tended too. She recovers slowly as mobility in her arm remains limited even after her procedures. John visits her to tell her what he learned of their pasts and Halsey's involvement in kidnapping them as children for the Spartan program. Their bodies were swapped out with genetically flawed flash clones so their parents could 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 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.
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.
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.
- Halo: The Television Series