Haruto Souma is a central character in the anime who serves as a childhood friend and emotional anchor to the protagonist, Eita Izumi. A third-year high school student, Haruto is a member of the school’s baseball team and has already secured a job at a factory following graduation, a decision that sets him apart from peers who are focused on university entrance exams. Physically, he is depicted as tall with black hair and yellow eyes, often conveying a wide range of emotions through expressive facial reactions.

In terms of personality, Haruto is initially presented as a straightforward and somewhat brash friend, but beneath the surface lies a deep vulnerability and anxiety about the future. He harbors a fear of becoming like his mother, whom he perceives as working endlessly without joy, and worries that his own life after high school will be devoid of meaning or excitement. This fear fuels his primary motivation throughout the story: to find a sense of purpose and a reason to keep striving. His answer to this anxiety manifests as a romantic pursuit of Hazuki Morikawa, a classmate in the concert band. He confesses to her because hearing her play the trumpet gave him a feeling of support, leading him to believe that a relationship with her could give his sacrifice of a carefree youth some meaning.

Within the narrative, Haruto plays the role of Eita’s best friend, often acting as a sounding board and offering advice, though he also seeks support from Eita in return. Their friendship is a key relationship, defined by a shared history in middle school baseball where Eita was the pitcher and Haruto was the catcher. Haruto is also aware of Eita's long-standing feelings for Mio Natsume, making him a confidant in the story's central romantic entanglements. His own story is largely driven by his relationship with Hazuki, a reserved and practical girl who is preparing to leave for a distant college.

Haruto’s character development is centered on his response to rejection and his confrontation with his own insecurities. After his initial confession to Hazuki is turned down, he sinks into a period of self-pity, feeling like a loser and attempting to discard his baseball glove as a symbol of his failed ambitions. He is pulled out of this state by Eita, who returns the glove as a reminder not to give up. A turning point occurs when Haruto plays in a baseball game for the factory workers; he realizes that they play with passion and joy despite their mundane jobs, showing him that a person is not defined solely by their career. This experience grants him the courage to face Hazuki again. Although she rejects him for practical reasons, citing their diverging paths after graduation, the closure allows Haruto to accept his situation with grace and maturity. His arc concludes with a tentative, hopeful note for the future when Hazuki asks him to wait until her college life settles down, at which point they might try again.

Notable abilities for Haruto include his athletic prowess as a baseball player, specifically his skill as a hitter, which serves as a metaphor for his emotional journey of taking big swings at life's challenges. He is also depicted as a loyal and observant friend, possessing the emotional intelligence to understand the dynamics between those around him, such as noticing the natural chemistry between Eita and a younger student, Ena Komiya.