|Slaughter each other as much as you want after that! Marleyans, Eldians, kill whoever you like! Just please, don't get my little brother involved in this!|
|— Colt begs Zeke Yeager to delay his attack|
Colt Grice (コルト・グライス Koruto Guraisu?) was an Eldian living in Marley and the older brother of Falco Grice. He was a Warrior candidate (戦士候補生 Senshi Kōho-sei?, also translated as "Warrior Cadet") who was selected to be the next wielder of the Beast Titan power before his death.
Colt was a physically fit young man with light eyes and short light hair. Like his fellow Warrior candidates, he wore the standard Marleyan soldier uniform consisting of a light jacket and pants, supply packs on the hip, suspender straps, a hard hat with a stripe around it, and tall combat boots. As an Eldian, his uniform was different from that of the Marleyans, as his shirt collar has a small badge of the Eldian star instead of a small clip and his helmet has the same star with a brightly colored stripe instead of a pure black stripe. As is law in Marley, Colt also wore an Eldian armband as all his family and ancestors residing there did.
Colt was a dedicated and brave soldier, risking his life to go retrieve his wounded brother Falco Grice after he came under enemy fire. He showed great care for his brother as he gave him his hard hat as they fled and made sure his wounds were treated when they returned to the hiding trench. While caring and brave, Colt was also a tactical soldier who worked with his Commander to plan their attacks, despite his superior officers looking down on him for being an Eldian. Colt always appeared to have a guess of what moves might be made in advance by the enemy and tried to strategize to use their forces and the power of the Titans to take out the threat without losing lives.
However, he lacked discretion in times of leisure, having Pieck Finger share her alcoholic drink, despite being very bad at handling liquor.
In 832, disgrace was brought upon the Grice family when his uncle's involvement with the Eldian Restorationists came to light. To prove his family's innocence, Colt was forced to pledge service to the Marleyan military as a Warrior candidate, eventually being chosen as the next inheritor of the Beast Titan.
During the Marleyan war with the Mid-East Allied Forces, Colt is present among 800+ other Eldians fighting on behalf of Marley. However, he is valued as a Warrior candidate with the potential to inherit the Beast Titan. During the fight, Falco Grice and some of his comrades are hit by enemy fire, killing some but sparing Falco and leaving him wounded. Colt appears to save him and puts his hard hat on Falco's head before carrying him on his back while avoiding enemy fire. When Colt returns to the hiding trench with his wounded brother, their fellow candidates tend to his wounds. Commander Theo Magath shows concern for Colt's well being but then demeans him when he reports that they are unable to dig any further due to enemy fire.
Colt voices concerns over the enemies' artillery, saying they should let Porco Galliard and Pieck Finger handle the enemy gunmen, but Magath refuses. The appearance of the anti-Titan artillery leads Magath to order his 800 Eldian Warriors into battle to take it out, but before this can happen, the plan is canceled in favor of Gabi Braun's idea to solo attack it with a bomb. Colt watches as Gabi executes her attack and succeeds. When she is under fire from one remaining survivor, Falco rushes out of the trench to save her, much to Colt's concern. Luckily, the two are both saved by the transformation of Galliard and the last enemy gunmen is taken out.
After the war, during the meeting of the high-class officers, Colt is seen behind Zeke Yeager, who refers to Colt when he talks about the resume of Paradis Island Operation. After the meeting, Colt is seen talking to Zeke and discusses his Beast Titan's Power. Just as Zeke is about to unveil his secret, Commander Magath appears and stops the current conversation as Colt lights the cigarette for his superior. Later, he is seen drunk in the train as he praises Gabi for her bravery of taking the Armored Train down in place of 800 candidates.
Colt is later summoned to the Warriors' headquarters, where he attends a meeting with the current Warriors to discuss the dangerous position Marley's weakened state puts the Eldian people in, and Zeke's plan to resume the attack on Paradis Island.
After a month has passed, he attends a strategic meeting to determine how best to strike at Paradis Island. While there, he bears witness to his brother beating Gabi in a sprinting exercise. However, he claims it is too late for Falco to overtake her, for which Zeke mildly berates him. The two comrades are later seen playing catch, preparing Colt for his role as the next Beast Titan. Later that day, some time before the curtain at the stage rises, Colt wonders where Falco is shortly before the latter arrives out of breath and asks for Reiner Braun to come with him.
At his seat, Colt notes the number of high ranking officials, ambassadors from other nations, and reporters who have all come to Liberio for Willy Tybur's stage festival; admiring what the Tybur family is capable of. After the play on stage starts, Colt and his fellow Warrior candidates are left stunned when Willy reveals the truth behind the Great Titan War having been put to an end by the 145th King, Karl Fritz. He continues to listen with the others as Willy continues his speech. When Willy declares war on Paradis Island, he witnesses Eren Yeager's Attack Titan burst through a nearby building and crush the stage, killing Lord Tybur and sending debris into the crowd.
Colt is quick to act, pulling Gabi and Udo to their feet. He attempts to drag them away from the area, but when Udo spots Zofia's corpse, he pulls away from Colt's grasp. He reaches out for Udo, only for a stampede of panicked crowd-members to carry Colt and Gabi away, trampling Udo in the process. Colt and Gabi are forced to take cover behind a rock, until the pandemonium passes. Later, after recovering Udo's battered form, Colt and Gabi rush away from the stage, now a battlefield between the Attack Titan and War Hammer Titan. He expresses shock in the manner that Marley has been thrown into another war, when Gabi asks about Udo. He neglects to give her an answer, but instead tells her that they need to rush to a hospital. At this time, he starts to fret over where Falco is.
They reach a hospital and Colt begs a doctor to take a look at Udo, but the doctor refuses, stating that their beds are full and Udo is already dead. Disheartened, Colt puts Udo's corpse on the ground and asks Gabi to stay with her family and get as far away from the plaza as possible while he goes to look for Falco, ensuring her that the Warrior Unit will defeat the invading Titans. However, Gabi refuses, and says that she will go to fight too, because she cannot understand why Udo and Zofia were killed. She then runs towards the battle zone, as Colt vainly tries to stop her. He catches up to Gabi and Falco much later but is unable to stop them from using an enemy soldier's gear to get on board the airship and simply watches as they get away.
Colt later takes part in a meeting with Theo Magath and the other Warriors. He is alarmed after hearing of Zeke Yeager's betrayal and Magath's plan to attack Paradis Island alongside the Global Alliance. He then asks if they should have to wait that long to rescue Gabi Braun and Falco Grice before Reiner Braun declares they should launch a surprise attack now.
Colt takes part in Marley's retaliation attack against Paradis, stationed aboard one of Marley's airships. He parachutes into Shiganshina with Magath and a group of soldiers, meeting up with Pieck Finger and Gabi in the district. He is horrified to learn from Gabi that Falco has consumed Zeke's spinal fluid and been imprisoned by the Paradis military. Gabi further tells them about what she heard on the airship and Colt is stunned at the possibility of Zeke possessing royal blood. As Zeke joins the battle to aid Eren Yeager against Marley's Titans, Colt orders Gabi to board the airships Marley will be using to retreat while he goes to rescue Falco. Although he tries to dissuade her, Gabi vehemently insists that she will help him.
Arriving at the district's military headquarters, Colt and Gabi find Falco but are forced to stay out of sight of the soldiers with him. One of the soldiers with Falco spots them, but Gabi stops Colt from engaging him. The soldier discretely brings Falco to them and orders them to get him to safety before returning to his comrades.
The three take refuge in an abandoned building and Colt demands to know how Gabi knew to stop him from engaging the soldier. Gabi admits that she has learned that the Eldians on Paradis are simply normal people, leading Falco to admit to his unwitting role in Eren's attack on Liberio, much to Colt's horror. As Falco begins to lament that he will soon be transformed into a Titan, Colt assures him that if they can reach Zeke and let him know about Falco's condition, it is possible Zeke will not transform him.
Reaching Zeke right before he lets out a scream, Colt reveals that Falco had ingested some of his former superior's spinal fluid, and thus, he begs Zeke to wait until Falco is well out of range before screaming. He declares that he does not care what happens to anyone else currently on Paradis, Eldian or Marleyan, as long as Falco is saved. Zeke is sympathetic to Colt's dilemma due to both of their desires to care for their younger brothers and calls it a shame, but nonetheless, refuses to wait and lets out a scream. Colt, overcome by grief, hugs Falco and promises to always be with him as his brother starts to transform into a Titan. His close proximity to Falco's transformation causes Colt to be dismembered by the blast and ultimately burned to death.
- Falco Grice - Colt was Falco's older brother and cared deeply for him, as he threw himself into the battlefield to rescue his injured brother, even giving him his hardhat as they fled. After he witnessed Falco surpassing Gabi in a footrace, Colt expressed concern over the possibility that Falco will become a Warrior too. After learning that Falco had inadvertently consumed Zeke's spinal fluid, Colt did everything he could to try and save his brother by pleading with Zeke and even stayed with Falco as his transformation began, despite knowing it would kill him.
- Zeke Yeager - As a candidate to inherit the Beast Titan's power from Zeke, Colt greatly admired Zeke and his Beast Titan's unique ability to create and control Titans. The two had a mentor/protégé relationship with Colt standing by his side in important meetings and even playing catch together. Colt was alarmed when he found out Zeke betrayed Marley as the man he saw as a mentor had abandoned and betrayed him.
- Theo Magath - While Commander Magath may have looked down on Colt for being an Eldian, he valued him as a soldier and showed concern for his well-being when he risked his life to save his brother. Colt appeared to show some margin of respect for this man, as he attempted to work through strategies with him and was not above giving his opinion on the best move.
- He shares a birthday with the Trost District citizen.