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Brawny and blond, Reiner's physique is exaggerated to the point of having a well built chest and defined arm muscles. He wears the standard uniform of the school.
He has a tough physique and can be stubborn. He gave his heart to Christa but is always chased away by Ymir. He is seen hanging out with Bertholdt, often giving him helpful advice about being more confident or speaking out. In the class's eyes, Reiner is often admired for his assistance and supportiveness.
Reiner attends his first day of school. He introduces himself to the class and is called out to the courtyard for the entrance ceremony. Reiner finds his friends complaining about their clubs and he pitches in. He advocates that they are going to have to live with it, as he is facing a similar situation. 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.Reiner participates on Annie's team in the game of dodgeball. With his teamwork along with the members, the team manages to win their first match easily. When the ball hits Christa, he rushes for her safety. So happen, Ymir is on guard as she trips Reiner and catches the ball, gaining the praise from Christa in her own hands. On lunchtime, him along with his teammates, offers their Mozuku Seaweed lunch to Annie. Later on the continuity of the match between Mikasa, Annie and Eren, he bets on Annie with some snacks.
Reiner trains with a student in the Judo Club. 
- Bertholdt Hoover - Reiner believes that Bertholdt should not be afraid of trying to stand out. He shows this by trying to make Bertholdt more well-known among his peers or trying to make him comfortable with talking to others.
- Christa Lenz - Reiner has an unrequited crush on Christa. He is easily charmed by her acts of kindness and is nervous around her, however it appears that Christa does not pay much attention to it.
- Ymir - Ymir is the stopper between Reiner and Christa. She disapproves of Reiner's crush on her and tries to block any interaction between them.