Eren has messy brown hair and teal-green eyes. Along with the other students, he wears the school's standard uniform that features black pants, a black jacket, a white long sleeve shirt, and white shoes.
Eren vows to kill every single Titan that stole his favorite lunch—cheeseburgers. He idolizes Levi and so decides to join the club he is in. Eren is an overall disorganized person who can be clumsy, reflected on the first day of school when he overslept and had to rush to school.
Eren wakes up from a long dream, drooling. Mikasa wakes him up, but he panics enough to get himself dressed quickly, scared that he will be late for his first day. He is so distracted by his conversation with Mikasa he does not notice Christa and accidentally crashes into her. He apologizes by giving her little money to make up for making her drop her breakfast. Ymir splits them up and sends Eren and Mikasa off. Eren crashes into Sasha next, damaging her watermelon in the process. He gives her a small picture of him to apologize, and she demands he pay for her watermelon. Afterward, he collides with Mikasa at an intersection and is sent flying to the doorstep of Titan Junior High School. He finds the people from before trailing behind, all angry at him. However, they all hear the school bell and try to find their class. Eren accidentally runs into the Titan part of Titan Junior High, and tries to find his class 1-4. There, he is attacked by the dropping of giant stationery and notices that it belongs to a Titan. Everyone scrambles out of the classroom and are luckily found by Hannes.
Eren is properly directed to his actual classroom, where he passionately introduces himself as the person who will eradicate Titans from the entire world. Eren's thoughts are intercepted by Jean, and they start fighting. Mikasa breaks up their fight and Jean blatantly shows his jealousy of Eren. Their fight is stopped by their teacher this time. Later on, Eren assembles with the rest of the first years to get welcomed by their Colossal Titan principal. Eren sees that their principal has kicked a hole in their school Wall and Titans are invading, stealing people's lunches. He angrily grabs cleaning supplies as weapons and charges at the Colossal Titan by jumping off a roof, but falls to the ground mid-jump. The Colossal Titan steals his cheeseburger lunch and Eren is distraught.
Eren tells his classmates that Armin is absent due to the cold weather despite it being spring. With that in mind, he decides to go check on him later. Mr. Keith notifies him and his friends to give in their club admission forms by the next day or else they will be sorted into a club of Mr. Keith's own choosing. Eren and Mikasa finish buying meat buns and sweet drinks for Armin, however, their food is stolen by a Titan. To their surprise, Levi comes to their rescue by knocking the Titan down and Eren is inspired by Levi's actions. He asks which club Levi is in, however, Levi keeps that a mystery. Eren and Mikasa enter Armin's abode and have trouble getting him out of his room until Mikasa mentions the food they brought. Soon enough, Eren notes that there is a rip in Armin's futon. When Levi snatches Armin's futon away, Eren and Mikasa head downstairs to look for him. Mikasa finds a wings of freedom button belonging to Levi, so Eren suggests they look for him at school.
They easily find the club Levi is in, namely the Attack Junior High Scout Regiment and try to look for Levi there. Eren meets a variety of upperclassmen and is keen on joining the club. He asks about Levi's button, and Hange shows Eren a technique to summon Levi by throwing a plastic bottle in the wrong assorted bin. Levi smacks Eren in the head with his paper fan and returns Armin's futon. Eren recovers quickly and is convinced to join the club. Eren and his friends are approved for admittance, but Eren is assigned to the Wall Cleanup Club due to the Attack Junior High Scout Regiment being unauthorized.
Eren is excited for the next day's dodgeball tournament and is confronted by Annie, threatening him. The following day, he oversleeps causing his group mates to do sacrificial ways in order to win. In the midst of Jean being almost caught disguising as him, Eren arrives. Mikasa runs to him, warning Eren that being late is not a good practice. The game continues as Annie attacks; Eren gets face smashed, and Mikasa trying to keep him safe. With the three of them left, Eren charges the ball to Annie as she forcefully kicks it back to him, sending Eren flying to the air. As he comes back to his senses, Eren asks Annie about her hatred of him. Annie reasons out her denial of her love to cheeseburgers as the cause of her grudge against him. Eren offers up a hand, apologizing to her as they make up.
Next day at lunchtime, Eren drops his only cheeseburger for lunch. Annie requests to join him and his friends for lunch as she gives a cheeseburger to him. Eren is delighted and Annie offers another one, only for Mikasa to shove fish into his mouth. Eren assumes the act as Mikasa treating him like a child.
Due to the illegitimate approval of the Scout Regiment Club, Eren and the others find themselves cleaning the new building's windows from the orders of the Wall Cleanup Club's president, Rico Brzenska. Eren mocks himself for being a loser and envies the other students in much more fitting clubs. Irritation surges through Jean as he leaps off the window, with Eren and the crew reminding him that they are in the 3rd floor of the building. Afterward Rico takes down an escaping Jean, she introduces the omni-directional mobility gear to the group, catching Eren's attention. Jean and him fight over the gear as Rico declares an agreement to teach them if they have done their task. Moments after, Rico checks on them only to be approached by a bright light coming from the windows thoroughly cleaned. Rico then proceeds onto her promise with Eren and the gang.
Unluckily for him, Eren finds himself hanging upside-down from the gear. He goes through a repetitive process of banging his head and fails to use the gear properly. Mikasa tells him to give up, but Eren declines, recalling the thoughts of previous Titan attacks that brings him to the goal of their total destruction. Eren is enraging until Armin points out that it can be a possibility that a broken gear is handed to him, thus the cause of his infinite fall. As Mikasa glares at a mistakenly assuming Rico, Hannes comes over and teaches Eren the right way to use the gear. Tough-luck the gear busted and Hannes collides with Jean causing them to topple on top of each other. Hannes confronts Eren, saying he lacks the experience and reasons out his own failure due to drunkenness. Rico hurriedly points out the broken gear and dismisses the activities.
The next day, Eren is able to balance on the gear, thinking to himself that Mikasa should stop treating him like a child. On the other hand, Mikasa explains Eren's happiness is because he can now clean the Wall with her. Suddenly Sasha senses trembling which originates from a bunch of Titans heading for the Wall. Eren along with Rico and the gang take cover behind the trees. Enraged, Eren grabs off Mikasa's broom and attempts to attack one of them. Unfortunately, his gear runs out of gas and Eren smashes through the paintbrush dipped in red paint. Though he failed, Eren curses to eliminate the Titans once and for all.
In the morning of the test results day, Sasha finds herself flunking in all tests. Eren remarks that she freaked out about the fact that she would be denied lunch if she flunks the makeup tests more than when she first received her test results. She asks for his help in studying, but Eren says he has to go to the Scouts room. Arriving there, Eren, Mikasa, and Jean find Oruo lamenting his bad test score. Oruo asks for everyone to reveal their test scores at the same time, and Eren is surprised to see Oruo is only six points short from a full score.
At the end of a school day, Eren tells Mikasa that her hair is too long, saying it could cause an accident during gear training, with her replying that she will cut it. A jealous Jean suddenly grabs Eren's shirt, but Mikasa intervenes and stops the fight by picking up Eren and carrying him outside. The next day, Eren is shocked to see Jean with a new hairstyle, and he reveals a love letter he had received the day before as being the reason for his new "cool" look. Eren points out that the letter is not signed, and Armin mentions the possibility of it being a prank, to Jean's anger.
Later on, Eren and the others find Annie running away after putting something in Jean's locker. Jean finds it to be another love letter, with this one stating a meeting at the park. Accompanying Jean, Eren and the others are left shocked when Annie suddenly screams and summons her Titan friend, which the letters had been from. Eren questions Annie of her friendship with a Titan, and she says they both attend the same cram school. Eren and Marco then both try to talk some sense into a delusional Jean, as he starts accepting a relationship with a Titan, but ultimately snaps out of it and rejects the idea.
Eren advises Jean to stop skipping the Wall Cleanup Club's activities, since Rico was upset. Eren and the others are then stuck cleaning every window in school because of Jean. Arriving late at the Scout Regiment Club room, the upperclassmen chastise the group. As the upperclassmen start nitpicking over the group's way of dressing, Eren becomes dizzy and shouts for them to shut up. They are once again stuck with cleaning duty as penalty. Levi checks on the group and criticizes their cleaning, then decides on teaching them a lesson after Sasha and Jean talk back to him; everyone will compete in the Sports Day games, and the losing grade cleans the Titans' building.
Eren cheers for Sasha when she participates in the first game, the bun-eating race. He later participates in the last game, shoulder wars. As Mikasa's team distracts Petra, Eren successfully steals her bandana. Mitabi's team then charges Eren's, but Armin's team intervenes and tackles them, with Armin encouraging Eren to fulfill his responsibility.
As Eren's team presses forward, they are shocked to see Levi nonchalantly sweeping the playfield with a broom. He says they are in the way of his cleaning. Frightened by his confidence, Eren hesitates, but Reiner tells him not to back down, with Jean saying it is their only chance. Remembering everyone's sacrifices, Eren and his team charge forward, and as he tries to grab Levi's bandana, Levi strikes the whole team with his broom and sends them flying after stealing all of their bandanas. Eren and the others then clean the playfield after Hange releases a sea of confetti on it. After some of the upperclassmen arrive to help them, Eren and his classmates bow to them in regret and apologize for talking impudently earlier.
The upperclassmen plan a sudden "Test of Courage" event for everyone to strengthen their friendship after what Year 1 students did the day before. Eren wanders inside the school at night, and is frightened when a teacher suddenly grabs his shoulder and asks him a strange question. The teacher apologizes and introduces himself as Erwin Smith, the advisor for the Scouts club. After the rules are explained, everyone is assigned to a group, and Eren's group heads to the art room. Eren finds that the blackboard already has the names of another group, and as he and Jean struggle over who gets to write his name first, they hear a disembodied laugh from a painting. Armin points it to be the "Laughing Mona Lisa," No. 1 of the school's Seven Wonders. They all flee from the room in horror after the painting's face morphs, giving a sinister grin.
Arriving at the music room, the group suddenly hears the piano playing by a figure and Armin points it to be No. 2 of the Seven Wonders, Beethoven playing Symphony No. 5. Everyone starts throwing music instruments at the figure, and Eren is separated from his group after running off on his own. Catching his breath on a stairwell, Eren is frightened by his own reflection in a nearby mirror, before glimpsing a girl with long hair in it. As he tries to convince himself he did not see anything, the girl appears in front of him screaming, to Eren's horror. He regroups with the others in the science room, and as they wonder why Reiner's group did not pass by, Eren and Jean's shirts are pulled by two Titan models, making them run out of the room. Finally arriving at the gym, they are met by No. 6 of the Seven Wonders, the "Headless Dribbling Ghost." Eren and the others start running around as most of the Seven Wonders they saw earlier materialize and start chasing after them.
As a giant cannon chases everyone, Levi is irritated by all the commotion and hits the cannon, causing it to fall on top of Oruo. Levi then lands on top of the cannon and reattaches his head to his body, revealing his identity. The first years look down and recognize Oruo underneath the cannon. They also realize that the ghosts and models they saw were Petra, Eld, and Gunther when they took off their costumes.
Eren is relieved, but Erwin asks him about what he saw, stating the school's Seven Wonders No. 7 is a girl who went missing during a test of courage, and unaware she had become a ghost, is said to still roam around looking for someone to scare. Eren nervously denies he saw anything, and is then scared stiff by Mikasa killing a mosquito, as the ghost girl watches and smiles from afar.
Eren attends a summer festival with his classmates. Excited where to go first, he is reminded by Mikasa that his mother told him to use his allowance carefully. Arriving at a shooting game stall, Mikasa easily wins at the game from her first try, and chooses to gift Eren her prize; Big Pork Fillet Cutlet, saying he looked like he wanted it, and he asks her what kind of look is it. Later, Eren participates in die-cutting, but fails and cracks the sticker easily, with Bertholdt giving advice. Eren and his friends then watch in enjoyment as more festival fireworks are set into the sky.
After the student council scandal, an election is held for a new president, and Eren decides to run in the election, determined to destroy every last Titan. Jean confronts him and says he is gonna be the president, with Eren replying that Jean does not need to become president to keep that comfy fantasy of attracting girls in his head. As they are about to exchange fists, Mikasa lifts Eren on her shoulder and takes him outside the classroom. Eren is later surprised to find out that candidates need a poster. Armin tells him that they can make one back at his place. There, Armin shows Eren his poster's design on the computer, with Eren praising his skill. Armin says he can do a lot more. Eren then guides Armin for a few more tweaks, which result in a disfigured-like design of Eren's face. Armin and Mikasa are shocked, but Eren likes it and believes it will get him to win the election. He excitedly asks Mikasa of her opinion and Armin thinks to himself that Mikasa should tell him what she really thinks, but she replies that it looks good, to Armin's horror.
Outside, Eren proudly holds up his poster while walking to the board. After seeing Jean 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 had filled every board with his posters, and they both then put up theirs on top of his. The results of the opinion poll are out. Eren and Jean are shocked to see they both got 0%. After Hange mentions a notebook that could turn the tides in favor of whoever gets it first, Eren and all the other candidates head to seek it. Everyone chases after Ilse Langnar, the owner of the notebook. After a long pursuit for the notebook, it ends up in Rico's hands, and she reveals that it only contains cleaning tips.
When it is Eren's turn for his final presidential speech, Armin tells him not to say anything weird and he says not to worry. On the platform, Eren shouts that his reason for becoming president is to destroy every Titan in school, and in the whole world. The crowd starts booing. Seeing this, Armin talks to the crowd and advocates for Eren's presidency, momentarily succeeding before Eren started calling them cowards and to just vote for him. As the teachers are shocked by his rudeness, Levi suddenly appears and kicks Eren in the face, sending him flying off the stage. The election later concludes with Marco winning, to Eren and Jean's dismay.
With the school's 104th festival approaching, Eren decides for his class to participate in the gourmet competition by doing cheeseburgers. In front of the cheeseburgers stand, Eren happily remarks it is their chance to let everyone know how magnificent chee-burgs are. The chee-burgs stand becomes popular, and they are overwhelmed by tens of orders. Eren says even Mikasa cannot handle that many, and looking at Rico's stand serving customers faster, Eren laments the situation, before Mikasa says she can do it, and starts rapidly flipping multiple burgers at the same time. Armin notices their rivals' pot rice is nearly ready, and knowing their rice is what made them win last year's festival, he suggests a limited-time sale to Eren; doubling the amount of cheese for the same price. Eren and the others later hear a commotion from Rico's stand.
Realizing they are about to open the rice pot's lid, Armin starts promoting for the double cheeseburgers with double cheese for the same price, attracting more customers to their chee-burgs stand. Everyone is suddenly interrupted by loud trembles in the ground. A horde of Titans is approaching the food stands, and everyone starts evacuating the area. Eren helplessly tries to fight holding kitchen tools in hand, but a Titan steps on him. The Titans steal all of the food stands and then leave. Mikasa comes to Eren's side, and he cries out for his chee-burgs while cursing the Titans.
An enraged Eren tells Armin that he is going to the Titans' school building to retrieve their chee-burgs. When the teachers get in the way, his classmates come between them and stand up for him. Eren heads to the Scouts room seeking the upperclassmen's help. When Levi says they are on standby, Eren argues that if they act fast, they may be able to get back their chee-burgs. The other upperclassmen chastise Eren, and he then thinks to himself that he can fight on his own, wondering why he is always relying on others. As he tries to leave, he is stopped by Petra, but Levi then says that Eren is not wrong, telling him to choose whichever choice he would regret the least, then orders him to decide now, and Eren decides to move forward and heads to the Titans' building.
In front of the building, Eren vows to destroy every last Titan, then suddenly Eren and his friends are seen running away while being chased down by Titans inside their giant hallway. Hannes appears from inside a hole in the wall and ushers them in. They find Rico and Ian have brought the Wall Cleanup Club's gear with them. After putting on their gear, Hannes tells them that he will get the Titans' attention while they move forward. He heads out wearing the gear, but accidentally crashes into a window, breaking it and falling over. As Titans look over the window, the others use this chance to sneak out. Earlier, Hannes explained the layout and pointed the way to the principal's office, telling them that their chee-burgs may be in the door inside the office, though it needs a key.
Arriving at the principal's office, they are frightened by its door's size. Inside, Eren flies up to what seems to be a table, but is surprised to find it to be a walled town. Jean points out a huge key lodged in the middle of the town, and a door with a matching keyhole is further ahead. Ian warns them of four Titans approaching, and Armin tells Eren to pull the key out and open the door, while everyone else backs him up. Eren arrives to where the key is, but is unable to pull it. Armin then reminds Eren of his goal, asking him why did he want to go to the Titans' building, and Eren answers it is because he was born in this world.
Everyone then witnesses Eren carrying the giant key, slowly walking to the door. Armin tells Mikasa that they just have to cover him until he reaches it, and Ian orders everyone to defend him. Eren states to himself that when people are born, they are free despite the rules that deny that, and no matter how absolute the school rules are. Finally reaching the door, Eren, while being encouraged by Armin, inserts it and successfully opens the path inside.
Eren and the others arrive at what seems to be the gym, with a group of Titans inside it standing around all of the stolen food stands. Eren charges forward but Mikasa grabs him, and they all fall to the ground. As the Titans surround them, suddenly, a disguised Levi, Hange, and Miche forming a band start playing on a stage, attracting the Titans' attention. Sasha remarks that they came despite everything, but a clueless Eren says he does not know who they are but still appreciates the help, to everyone's exasperation. As Jean insults him and tries to tell him their identities, they are all interrupted by the principal, the Colossal Titan, opening the gym's roof. Armin then realizes that they are in fact inside the principal's lunch box.
As it grabs the chee-burgs stand, Eren faces the Colossal Titan, remarking that they had not met since the entrance ceremony. It ignores Eren and as it opens its mouth to eat the chee-burgs, Eren jumps at it and is swallowed as well. Everyone is looking in horror as Armin starts screaming and Mikasa falls to her knees. The Titan then spits Eren out, and he happily announces that he managed to retrieve a chee-burg. Back at their building, everyone is cheering and celebrating their victory while throwing Eren up in the air, as he happily bites into the chee-burg he retrieved.
- Mikasa Ackermann - Although Eren does not really pay attention to Mikasa's acts of affection towards him, he tries to get along with Mikasa despite her babying him. He acknowledges that she excels at everything she does and strives to beat her to prove his usefulness. As they were close since young, they have a casual friendship.
- Armin Arlelt - Armin is Eren's best friend, and they were friends since childhood. Eren tries his best to make Armin realize his potential as a person, despite being a current shut-in. Eren is very supportive of Armin's ideas, often encouraging him to voice his opinion when he wants to.
- Levi - Eren bluntly idolizes Levi from his strength as "the strongest man" to his role in the anonymous band "No Name." Simply put, Eren aspires to possess Levi's demeanor when defeating Titans and is dedicated to the Attack Junior High Scout Regiment after hearing such an individual took part in the club.
- Jean Kirschtein - The pair often argue a lot due to differing opinions and personalities. Even though Jean brags to Eren most of the time about his popularity in elementary school, Eren does not feel inferior to him.
- Grisha and Carla Jaeger - They are the parents of Eren who wish him a good day at school. Although their relationship is not fully shown, it is implied that they are very close as a family.