|It was a direct hit. The Eldian unit at the front got blown away.|
|— Colt tells Theo Magath the situation|
Colt Grice (コルト・グライス Koruto Guraisu?) is an Eldian living in Marley and the older brother of Falco Grice. He is a Warrior candidate (戦士候補生 Senshi Kōho-sei?, also translated as "Warrior Cadet") set to be the next inheritor of the Beast Titan.
Colt is a physically fit, tall young man with long face, light hazel eyes and short blond hair. Like his fellow Warrior candidates, he typically wears 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 is 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 brands an Eldian armband as all his family and ancestors residing there did.
Colt is 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 is 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 appears to have a guess of what moves might be made in advance by the enemy and tries to strategize to use their forces and the power of the Titans to take out the threat without losing lives.
Colt is shown to be very irresponsible when not on duty, and is well known among his allies for his penchant for alcohol.
Colt and the Warrior Candidates are part of the Eldian force dispatched to attack Fort Slava at the end of the Marley Mid-East War. During the fight, Falco Grice is injured by enemy fire and Colt is forced to carry his brother back to Marley's trenches. Upon their return, their fellow candidates tend to Falco's wounds while Colt reports to Commander Theo Magath. 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, suggesting that Porco Galliard and Pieck handle the enemy gunmen, but Magath refuses. After Gabi manages to destroy the fort's anti-Titan artillery singlehandedly, Falco leaves the trenches to try to help her, to Colt's alarm.
After the war Colt, as the candidate who will inherit the Beast Titan next, attends a meeting with Zeke Jaeger and Marley military's high-ranking officers. After the meeting, Colt talks to Zeke about his Beast Titan's power, marveling at Zeke's unique ability to create Titans. Their conversation is halted when Magath arrives.
While the Eldian unit is returning to Marley via train, Colt gets drunk and begins to praise Gabi for her bravery in taking the Armored Train, starting a celebration among his fellow soldiers. The train arrives at Liberio the following day and Colt, hung over, needs has to be helped off the train by Galliard. Back in the internment zone, he meets his parents.
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.
Colt attends a strategic meeting to determine how best to strike at Paradis Island. After the meeting, he and the Warriors witness Falco beat Gabi in a sprinting exercise. Colt notes that it is already too late for Falco to improve his grades enough to surpass Gabi.
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 Jaeger'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.
After recovering Udo's battered form, Colt and Gabi rush away from the stage, with Udo's body. 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. However, Gabi refuses and runs towards the combat zone to help fight as Colt vainly tries to stop her.
Colt takes part in a meeting with Magath and the other Warriors. He is alarmed after hearing of Zeke's betrayal and Magath's plan to attack Paradis Island alongside the Global Alliance. He asks if they should have to wait that long to rescue Gabi and Falco before Reiner declares they should launch a surprise attack immediately.
Colt takes part in Marley's retaliation attack against Paradis, stationed aboard one of Marley's airships.