Along with an arrogant smile plastered on his face, Jean has a two-toned undercut and wears the school's standard uniform.
Jean is in the same class as Eren and Mikasa. He gets into fights with Eren often and has a crush on Mikasa. He sees himself as a genuine intellectual and appears to be wealthy. Jean enjoys bragging to his peers about his popularity in elementary school. Jean clashes with mostly everyone in his class, as he believes that he is above most of them. He acts obnoxious towards girls, so some ― if not most ― find him repulsive.
Eren bumps into Jean on the first day of school. He calmly ignores Eren and proceeds on hurrying to school. But as soon as Mikasa steps over him, he becomes fascinated. Lagging along with the rest of the group chasing Eren, he ends up in the Titans' side of the school. As he proceeds to drag behind with Eren neglecting his suspicions, he is greeted with a shower of gigantic school supplies. Spotting a Titan behind them, he hurriedly rushes away. Much to his perverted thoughts of pulling down Christa's skirt, he ends up dragging down Conny's pants. Along with Sasha, Eren, and Conny, they go tumbling out the door. Luckily, they are found by Hannes who directs him and the others back to the humans side of the school. Jean stirs up a fight after Eren introduces himself to the class. He notices Mikasa trying to break them up and is dumbfounded by her beauty. Out of jealousy, Jean has another go at Eren but this time he is stopped by their homeroom teacher. Jean later attends the entrance ceremony.
Jean wonders why the person sitting next to Eren has been absent for a long period of time. That turns out to be Armin, who is properly introduced to him later. Jean follows his friends to find the Attack Junior High Scout Regiment, where he is accepted into said unauthorized club. The next day, his name is signed up for the Wall Cleanup Club by Mr. Keith, who assigned them to a random club because they did not send in their admission forms.
Jean takes part in his school's dodgeball tournament and is confident in his team's abilities - especially Mikasa's. To his dismay, Eren is late which causes Mikasa to lose energy and the will to play. His friends suggest Jean dress up as Eren to temporarily fool Mikasa in order to play against Annie's team, however, their plan ends up failing. Luckily, Eren appears in time for the match. Jean watches in awe as Mikasa's performance is equal to Annie's, ensuring them a higher chance of victory. Dazzled by the match, he forgets to dodge an incoming attack, taking him out of the game.
Along with the gang, Jean is forced to clean the windows under the orders of the Wall Cleanup Club's president, Rico Brzenska. Irritated by the passerbys, Jean admits to himself that popularity is his sole goal and cleaning does not help to reach it. He lunges out the window, remarking to the others that he will choose to follow his goal. Upon landing, shock sends through Jean not noting that he jumped from the third level of the building.
With an attempt to escape, Rico catches him and brings Jean down. Upon Rico's introduction of the omni-directional mobility gear, Jean thinks of many possible ways to use the device in order for him to get popular. He and Eren fight over the gear as Rico notes the both of them as idiots. The president makes a deal that if they finish the task assigned to them, she will teach them how to use the gear. With that said, Jean and the rest rush to get their job done.
While Eren struggles with his gear, Jean mocks him with his redundant determination to do such things. With the club's adviser, Hannes tries on Eren's busted gear and attempts to fly. Unfortunately, he crashes into Jean causing the two to tumble to the ground. Rico appoints the broken gear and that dismisses the activity. The next day, Jean and the rest are happy for Eren's success in using the gear. As Sasha senses a tremble on the ground, Jean and the group hide among trees. Jean witnesses the horrible scene of Titans vandalizing the Wall. He discovers the real reason behind the Wall Cleanup Club's main purpose.
The day of the test results, Jean mocks Sasha for failing then goes to the Scout Regiment club room with Eren and Mikasa. They are greeted by Petra Rall and her classmates. Upon hearing Oruo's complaints about his grade, everyone shows theirs to compare, much to Jean's annoyance. Later on, he helps Eren and Gunther restrain Hange who was starving and had attacked Oruo for his lunch money. When Hange introduces the first years to the two Titans she has captured, Jean is horrified and tells her bringing up Titans is not possible.
Jean and Marco walk into the school hallway and they come across Conny and Sasha, then Franz and Hanna. Jean calls the two a stupid couple and gets upset at their reaction. He then sees Eren and Mikasa together, which angers him and he grabs Eren by his shirt, telling him how jealous he felt. After that, he complains about girls not noticing him and opens his locker to find a love letter. The following day, Jean comes to school with a different hairstyle and perfume on him. He boasts off in front of his classmates and proudly shows them the letter.
After having read it again, Jean begins to think the author of the letter must be a girl close to him. Looking at the girls around him, he then imagines Sasha, Christa, Ymir, Petra and Rico showing interest in being with him and even fighting for it. He then looks up to Mikasa, at first assuming it would be unlikely, then imagining her being in love with him. Jean is then approached by a blushing Annie who wants to talk to him. Mikasa and her begin to argue, which makes Jean assume they are fighting for him. As he proudly tries to calm them down, the two girls hit him. In her movement, Annie lets down a letter which looks exactly like the one Jean received earlier, which makes him believes she has feelings for him.
Later on, Jean and the others see Annie putting something in his locker. Annie suddenly leaves and Jean goes to find a letter which asks him to go to the park. Once he arrives there, he impatiently waits, then Annie comes with the others. Jean tells Annie he agrees to date her, which angers her. As a consequence she hits Jean before explaining she wrote the letters for a friend of hers. Annie then calls her friend and Jean learns that a Titan is in love with him. Annie explains the reason for her friend loving Jean, and Marco remembers a day when they were chased after by a Titan that stopped when Jean threw his bento in its mouth. Jean is at first shocked by the news but then tries to persuade himself that the Titan is actually human and forces gestures of affection towards it. After Marco yells at him, he comes back to reality and admits he does not want to date a Titan. In response, the Titan cries, hits him and runs away.
Jean is now feeling down so, in order to cheer him up, Sasha takes her white radish and her curry bread and makes them talk like they were two women fighting for Jean. This works, as Jean takes the food and imagines two women are fighting for him.
Jean skips the Wall Cleanup Club's activities without permission, resulting in Rico ordering him and the others to clean every window in the school. Arriving late at the Scouts club, the upperclassmen start nitpicking over the group, with Eld scolding Jean for wearing a colored undershirt. They are later stuck with cleaning duty as penalty again. After Levi gives the group a challenge, Jean participates in the school's Sports Day. In the ball-tossing game, Jean cheats by using the Wall Cleanup Club's gear, maneuvering around the balls. Rico yells at him not to use it without permission, while deflecting a ball towards him and he falls after being hit by a barrage of balls. Rico's team then surrounds Jean and beat him up at her signal. In the last game, shoulder wars, Jean teams up with Eren, Reiner, and Bertholdt. When they charge at the Year 3 leader, Levi, he hits and sends them all flying after taking all of their bandanas.
The upperclassmen plan a sudden "Test of Courage" event at night. Jean is assigned to Eren's group and they head to the art room. As he and Eren struggle over who gets to write his name first on the blackboard, they hear a disembodied laugh from a painting. They all flee from the room after the painting's face morphs into a sinister grin. Arriving at the music room, the group suddenly hears the piano playing by a figure, and everyone throws music instruments at it. In the science room, Jean and Eren's shirts are pulled by two Titan models sneaking behind them, making everyone run out of the room. They head to the gym and they all start running around as ghosts and a giant cannon appear chasing after them. It is later revealed that the event is a prank played by the upperclassmen.
In the morning, Jean comments on one of Bertholdt's funny sleeping positions. He later goes to the summer festival with his friends. When Conny and Sasha take too long in getting back after buying the group shaved ice, Jean argues with them since it had melted. He later participates in die-cutting with the others while watching more festival fireworks set into the sky.
Following the news of an election for a new student council president, Jean confidently decides to run for it, believing that girls would be going crazy for him if he wins. Hearing Eren also running, Jean confronts him and the two are about to exchange fists until Mikasa intervenes. Jean barges into the student council club and Hitch hands him the application paper. Seeing he has to sign, Jean tells Hitch that she must like him since she wants his autograph, making her hit him in the head.
Jean later carries his election poster heading to the board. Seeing Eren in the way, they clash and ask if the other came to put his poster up, but are shocked to see that the whole board is filled with one poster; Oruo's. Oruo tells them that he has filled every board with his posters, and they both then put up theirs on top of his. In the opinion poll results, Jean finds that he got 0%. He and the other candidates later start chasing after a notebook that allegedly contains info which could help them win the election, only to later discover that it merely contains cleaning tips.
When it is Jean's turn for his final presidential speech, he nonchalantly tells the crowd that he wants to become president so that girls could like him, and the crowd boos. The election concludes with Marco winning after he delivers a speech standing up for Jean, much to Jean's dismay.
In the school's 104th festival, Jean participates in a Snow White play as the Queen. However, when Armin fails to switch places due to being occupied with Eren's cheeseburgers stand, Jean is forced to play his role as Snow White, and subsequently the prince. As he reluctantly tries to kiss the Titan model dressed as Snow White, the audience rushing out suddenly makes him slip and he accidentally lands a kiss on it, to his horror.
Jean joins Eren and the others in pursuing their stolen chee-burgs from the Titans' building. After being rescued by Hannes, he points them to the principal's office and in there, Jean points out a key and a door is further ahead. Everyone distracts Titans while Eren pulls the key.
He comes to Conny's aid, headbutting a Titan in the back of its head. As another Titan lunges at Jean, a scream is heard and Annie appears from above with her Titan friend and it lands on the lunging Titan, saving Jean. As one last Titan stands in Eren's way, Jean is thrown at it by Annie's Titan friend, knocking it down. Eren successfully inserts the key and opens the door.
Inside, the Colossal Titan then lifts the roof and eats the chee-burgs stand along with Eren, but later spits him out and Eren reveals a chee-burg he retrieved, with Jean celebrating their victory.
- Marco Bodt - Marco is surprisingly patient with Jean and is one of the first students who politely welcome him to class. Notably, the two are best friends and support each other wholly.
- Eren Jaeger - Jean takes an immediate disliking to Eren the second he introduces himself to the class. Not only is Jean jealous of Eren's close relationship with Mikasa, he sees Eren as an imbecile with opinions that are the exact opposite to his.
- Mikasa Ackermann - Jean has an obvious crush on Mikasa. He goes dreamy whenever fantasizing about her, but is mostly nervous whenever he wants to speak to her upfront. He admires her and compliments her, blindly supporting her in anything she does.
- Peering Titan - Jean has a weird relationship with the Peering Titan as she fell in love with him when he threw his lunch at the Peering Titan's mouth.
- Hajime Isayama has said his favorite character is Jean.
- "Jean" is the French variant of "John," meaning "Blessed by God." "Kirschstein" is a German surname meaning "cherry stone".