Bertholdt has shaggy dark hair and dark brown eyes. He is the tallest in Eren's class and also wears the same uniform as every male student in their Junior High.
He always considers himself to be overshadowed by Reiner and in turn, he does not stand out because of his beliefs. His gaze is always directed towards Annie, and is sooner known to have feelings for her. He also has a great talent for arts.
Bertholdt arrives to school on his first day and introduces himself to the class. Later, he is called out to the entrance ceremony where their principal, the Colossal Titan "welcomes" them by kicking the Wall open.
Bertholdt finds his friends in the school courtyard. He follows his friends to locate the Attack Junior High Scout Regiment, where he meets odd upperclassmen who welcome him into the club, despite being in a different one already.
Bertholdt takes part in the dodgeball tournament in Annie's team. Although his team is on a winning streak, Bertholdt ultimately goes down by blocking the ball before it hits Annie, sacrificing himself.
Bertholdt blocks the ball with his face in the practice of the volleyball club.
Later on, Levi challenges the group for the Sports Day event and Bertholdt participates with his class. The sight of Annie wearing a cheerleader costume makes his nose bleed. In the last game, shoulder wars, as Bertholdt charges with his team against Levi, he hits and sends them all flying after stealing their bandanas. After the class' defeat, the first years group clean the court then are joined by Rico and the Scout Regiment second years. The first years apologize for their disrespectful manners.
Following the Sports Day challenge, the first years group are invited by their Scout Regiment upperclassmen to do a test of courage at night. After Hange and Levi finish explaining the rules, Bertholdt leaves first with Reiner, Ymir, Christa, and Sasha. The girls go to the bathroom, leaving Bertholdt and Reiner to wait for them. Reiner sees something in the staircase, so he and Bertholdt begin to climb the stairs. Bertholdt continues to point out that the stairs seem to keep going, but Reiner says that it is Bertholdt's imagination. Later, when the rest of the first years are in the gym, Bertholdt and Reiner come crashing in followed by a huge cannon.
A few years back, a young Bertholdt, Annie, and Reiner are at a summer festival and Bertholdt shows his skill in die-cutting.
In the present, Bertholdt sleeps during class in an odd position. He is awakened by Reiner, who asks him to accompany him to the summer festival with Christa. Seeing Bertholdt staring at Annie, Reiner suggests that he invites her to the festival as well. His face becomes all red, and he quickly dismisses it and says there is not anyone he wants to ask, with Reiner remarking how of an open book Bertholdt is. He tags along with Reiner when he asks Christa if she would like to go to the summer festival with him and Bertholdt. When Christa agrees, Ymir then tells her that she had promised to go with her, and Christa says it will be more fun if they all go together. Annoyed, Ymir tells Bertholdt to say something, but notices his mind is somewhere else; looking at Annie.
She then approaches and tells him that she would be busy staying with Christa at the festival, so he should invite someone too, and again, Annie is named. Bertholdt reacts the same way he did when Reiner named Annie earlier. Reiner calls out for Annie this time and tells her that Bertholdt wants to talk to her. He panics and asks Reiner if they are really acting now, and Reiner says now is the time. Bertholdt stutters, but manages to ask Annie if she wants to go with them to the festival. Annie says she is not interested, but later yields when she finds out everyone is going.
A while later, on the school's rooftop, Reiner says he is glad Bertholdt was able to invite Annie, despite a bunch of unwanted people going with them. Seeing Bertholdt still not admitting it, Reiner tells him they should put an end to this with Bertholdt telling Annie how he feels about her at the festival, but he still denies it. Reiner tells him that he stares at her too much, to the point that anyone can tell, with Ymir saying the same, and calling him "Mr. Stare-thol." He then cowers in embarrassment, but Reiner tells him this is his chance to get close to her. Ymir then mentions the others getting in the way, but Reiner says he has a plan, as Bertholdt is thinking to himself that all he wants is to be by Annie's side.
At the summer festival, Reiner explains his plan saying that all Bertholdt has to do is compliment Annie by calling her cute. When Annie, Ymir, and Christa arrive, Ymir and Reiner tell Bertholdt to say something to Annie, and he compliments a knot on her geta strap, to Ymir and Reiner's disappointment. When the second plan fails, Reiner assures Bertholdt that he still has a trump card; Bertholdt protects Annie from staining her kimono. Later, Bertholdt asks the group if they want shaved ice, however, the wrong people went to buy it. Bertholdt suddenly tells Reiner to forget about the plan, saying it is not nice to put Annie in danger just for his sake. Just then, Conny and Sasha arrive with the shaved ice and Ymir takes the opportunity of Sasha and Jean fighting over a cup and pushes it towards Annie, with Bertholdt successfully protecting her.
As he washes up, Bertholdt regrets putting Annie in that situation. He sees a die-cutting table nearby. As the others split up and start looking for him, Annie finds where Bertholdt is. She stands behind him as he is die-cutting, and the owner praises his skill. He then hands him two masks as a prize, to Bertholdt's confusion, but he says it is for him and his girlfriend behind him. Seeing Annie, Bertholdt blushingly denies the relation.
Sitting nearby on a bench, Annie tells him that the others are supposed to meet up here once he is found. He apologizes for causing them trouble. Annie says he had always liked die-cutting, so she had a hunch he would be there, to his amazement that she remembered.
They both speak at the same time, interrupting each other. The others hiding behind bushes watch eagerly as Bertholdt asks Annie something as fireworks are set off, and she replies "okay." The others fall from the bushes and reveal themselves, with Reiner and Ymir congratulating Bertholdt, thinking he had finally asked Annie out. He then tells them they will go do die-cutting, to Reiner and Ymir's confusion. Back at the die-cutting table, Bertholdt participates with his friends, except for Ymir and Reiner, who let out a sigh in disappointment at the fact Bertholdt had merely asked Annie to do die-cutting. Bertholdt then watches in enjoyment as more festival fireworks are set into the sky.
Following the election for a new student council president, Bertholdt tags along with Reiner as the other candidates start chasing after a notebook that allegedly contains info which could help them win the election. However, after a long pursuit, they discover that it merely contains cleaning tips. Bertholdt later accompanies Reiner to the latter's final presidential speech on stage, and subsequently drags him off stage after he is faced rejection.
In the school's 104th festival, Bertholdt and Reiner visit the maid café room, with Christa serving them omelet rice. When Ymir spoils Reiner's meal, Bertholdt offers to switch his omelet with Reiner's. When Reiner burns his mouth trying it, Bertholdt realizes the omelet's insides contain hot sauce, and Ymir smirks while holding the sauce bottle. Bertholdt later helps Eren and the others at their chee-burgs stand.
When the teachers get in the way of Eren heading to the Titans' building to retrieve his cheeseburgers, Bertholdt and the others stand up for him and come between them. Later, after Eren manages to retrieve a chee-burg, Bertholdt celebrates their victory.
- Reiner Braun - In a way, Bertholdt looks up to Reiner's confidence with everyone, as he strives to be someone who can stand out just like him. As such, he often goes to Reiner for helpful advice regarding his timidity.
- Annie Leonhart - Bertholdt has unnoticed feelings for her that even some of his friends are aware of. He often dreamily stares at her or blushes when they share a conversation.
- Ymir - Bertholdt is often given love advice by Ymir or pushed into situations by her, albeit awkward ones, with Annie.