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Bertolt is a rather tall boy with short, dark hair. He can usually be seen wearing his school uniform while in class.
Bertolt is a very shy and quiet boy. He is shown to be very withdrawn in public, (often wishing that he stay in the background and not be as noticeable) and is usually only shown to have casual conversations with his friend Reiner. Bertolt can easily panic in social situations and can buckle under pressure; he is also known to have some self doubt and reluctant to reveal his feelings to others in fear of being embarrassed.
As revealed during an earlier event in his childhood, Bertolt is a notoriously bad singer. He himself is aware of this, but will still force himself to sing if there is no alternative (or one of his friends is reluctant to).
StoryBertolt is among the many first year students entering Attack Junior High School and is assigned to Class 3 along with his friends Reiner, Annie, Krista and Ymir.
He participates in the dodge-ball tournament and displays teamwork with his classmates when they easily advance to the second round; while not eliminating as many players, Bertolt is able to make several saves during the match. Despite his prowess, Bertolt and Class 3 are beaten by Class 4 who then advance to the finals.
Bertolt is with Reiner when the latter reveals the existence of the rumored Survey Club on campus. Bertolt joins the club with everyone and also signs up to be on the volleyball team as well. He takes part in the athletic fair pitting the first year students against the upperclassmen, but they are defeated and forced to dance with the Titans at the dance afterward.
A summer festival is announced and Bertolt is asked by Reiner to go with him and Krista. Caught by surprise by this proposal, the two hear Krista accept and insist Ymir go with them. Both Bertolt and Ymir are reluctant to be paired together, with the latter firmly stating she will be going with Krista. She confronts Bertolt about it and knows he was against the attempted pairing as well; Bertolt agrees and begins to think about asking Annie. Ymir, knowing Bertolt has a crush on Annie, insists he ask her or she will reveal to Annie about his crush. Reluctantly, Bertolt agrees to; he bemoans this and merely wishes to fade in the background. Despite this, he does go to Annie and ask her to meet him after school. After class, Bertolt starts to side-step the issue and reveals to Annie he is going with Reiner, Krista and Ymir; as he indirectly asks Annie to go with him as a date, Bertolt notices her attention is elsewhere. He spots her looking at Eren and sheepishly says she can invite someone to go with them if she wants.
After Bertolt informs them that Annie will be going with him, he learns from Reiner that the latter devised a plan years ago for Bertolt to use to win Annie's attention. This, coupled with how Krista mentioned Bertolt's crush on Annie is known by all the girls in class, severely embarrasses him and begins to second guess himself; Krista promptly slaps Bertolt and tells him to man up and be more confident. He remains uncertain but after the others promise to help him, Bertolt agrees to try his best. During the festival, Bertolt and Reiner are dumbstruck after seeing both Annie and Krista but before Bertolt can say anything, Eren arrives with many of his friends from Class 4. Bertolt begins to worry his chance is already over, but Reiner tells him to stay focused.
Throughout the evening, Bertolt tries to get Annie's attention but is ignored due to her trying to beat Mikasa for Eren's attention. Eventually Bertolt gives up his efforts and leaves the group, wandering over to a cookie cutting booth while crying to himself. Annie eventually finds him and they begin remembering their childhood. Bertolt is surprised when Annie remarks that she does not care about festivals and wonders why he asked her. As he tries to respond, Annie mentions that if Bertolt had not invited her, she would have left early and is comfortable around him; after they watch the fireworks for a bit, Bertolt turns to Annie and asks her to return with him to the cookie cutting booth. Feeling relieved that she agreed, Bertolt resolves to go to the festival again next year and returns to school the next day in high spirits. His friends, believing that he got over his confidence issues and asked Annie to be his girlfriend, applaud him but are stunned after he reveals he did no such thing. Krista immediately calls Bertolt a dumbass and starts slapping him again.
Later, Bertolt notices Annie watching Eren exercising with Mikasa and tries to get her attention. He mentions that while he might not be like Eren, he can do what he can do and offers to be Annie's exercise partner; he then shows off a six-pack he gained by doing abdominal crunches on a daily basis. However, Annie is not impressed and Bertolt is left gasping for breath after she punches him in the gut.
During the school's Culture Fair, Bertolt takes part in the bakery stall set up by the members of Class Three. However, due to one of the bands that entered in the Battle of the Bands not showing up, he is forcibly selected with Reiner, Annie, Krista and Ymir as their replacements. He laments how he is unable to take Annie's assigned position as singer to spare her embarrassment; seeing Eren cheering on Annie prompts Bertolt to suddenly step forward and take the mic from her. He begins to sing off-key and this quickly causes most of the audience (and his band-mates) to fall unconscious.
- Reiner Braun - His childhood best friend, Bertolt is almost always seen with Reiner. Bertolt admires Reiner's confidence and, while not as assertive, does see that Reiner is trying to build Bertolt's confidence and to make him more outgoing.
- Annie Leonhart - Another of his childhood friends, Bertolt has had a severe crush on Annie for some time; however, he is hesitant to reveal this to her. Whenever he is near Annie, Bertolt becomes easily flustered and unable to clearly speak; he does acknowledge that Annie has a crush on Eren and tries to improve himself to make him more appealing.