Junichi Aizawa is a secondary character in Handa-kun, serving as a classmate of the protagonist, Seishuu Handa. He is a second-year high school student known for his high intellect and strong leadership qualities, which have earned him the nickname the Chairman. Aizawa’s identity is deeply tied to his role as the class representative, a position he has held with great pride and responsibility for ten consecutive years, starting from elementary school. This tenure has made the role a core part of his self-image, and he is recognized as one of the smartest students in his class.

Aizawa is highly dedicated and serious about his duties, taking great pride in his work as class rep. His initial motivation is to maintain his position as the class chairman without any challenge. However, his world is disrupted when the highly popular yet reclusive Handa is nominated to run against him for the same position. Seeing Handa as a powerful rival, Aizawa becomes deeply concerned and employs various tactics, such as voting for himself, to secure his victory. This conflict is further complicated by a mutual misunderstanding, as Handa, who suffers from extreme social anxiety and paranoia, believes his nomination is part of a conspiracy against him and desperately wants to lose, while Aizawa is fighting just as hard to win. This absurd situation, where both candidates are working towards the same goal of Aizawa's victory, drives the comedy of their initial interaction.

Despite his initial skepticism and competitive stance against Handa, believing him to be a threat, Aizawa's perspective undergoes a significant change. By the end of the election arc, he comes to a profound misinterpretation of the events. Convinced that Handa taught him the importance of mutual trust and camaraderie, Aizawa develops a deep sense of respect and admiration for Handa. He willingly steps down from his long-held position, offering the role of class representative to Handa and instead becoming his deputy. This event marks a key development for Aizawa, as he transitions from a rival to one of Handa's most devoted followers. He forms a strong, albeit idolizing, bond with Handa, viewing him as a godly figure. Consequently, Aizawa becomes a core founding member of the self-styled Handa Force, a group of students dedicated to serving and protecting Handa, whose actions are based on a series of comedic misunderstandings.

Throughout the story, Aizawa is consistently portrayed as a highly intelligent student, a trait that is central to his identity as the class chairman. His primary ability, aside from his academic prowess, is his unwavering dedication and organizational skill as a class representative. However, his most defining trait is his serious and logical personality, which ironically leads him to completely misinterpret social situations and Handa's genuine, albeit neurotic, behavior, ultimately transforming him into an enthusiastic member of the Handa Force.