Armin Artlet is a first-year student at Attack Junior High School, maintaining a close childhood friendship with Eren Jaeger and Mikasa Ackermann. He has blond hair in a bob cut with straight-across bangs and blue eyes. His defining accessory is a futon named Bigbee, patterned with pink and yellow polka dot kitten heads, which he typically wraps around his body or occasionally drapes over his head. At school, he wears the standard uniform, sometimes omitting the black jacket.

Reserved and occasionally shy, Armin intensely dislikes cold weather, often staying home during winter. His room remains excessively heated, creating discomfort for others. Despite his timid nature, he provides mature perspectives and excels academically, achieving perfect test scores while assisting classmates like Sasha Braus with remedial studies.

His school involvement begins when Levi repairs his torn futon; after its return, Armin joins the Attack Junior High Scout Regiment club. He participates in dodgeball tournaments and Sports Day competitions, demonstrating loyalty by supporting Eren's team. During the summer festival, he assists at a cheeseburger stand and joins a mission to retrieve stolen food stands from the Titans' building. He also designs campaign posters for Eren's student council bid.

Beyond his core friendships, Armin maintains respectful interactions with Levi, recognizing the underlying kindness in his actions. He balances support and criticism toward Sasha, voicing disappointment when her focus wavers. Observant of interpersonal dynamics, he notes potential romantic tensions among Eren, Mikasa, and Annie.