Masahiro Hashimoto is the percussion instructor for Kitauji High School's Concert Band, recruited by his college best friend and classmate, band director Noboru Taki. An alumnus of Kitauji himself, Hashimoto was also once taught by Taki's father, Tooru Taki.

He sports messy brown hair, green eyes, and light stubble, standing notably shorter than Taki. Hashimoto explodes with colorful style: hot pink or yellow Hawaiian shirts, large blue glasses, a faux-leather watch, thin metal bracelets, and a yellow cord necklace define his look. His college self featured a letterman jacket and longer hair.

Fun-loving, athletic, and humorous, Hashimoto earns immense popularity with his percussion students. He peppers conversations with quirky interjections like "Hrm?" and insists students call him "Hashimo-chan." Thoughts often tumble out unintentionally, and he repeatedly—much to Taki's annoyance—offers tales of Taki's college misbehavior. Despite the levity, Hashimoto becomes a strict, demanding taskmaster during rehearsals, setting high standards mirroring Taki's own for the full band.

Perceptive of the band's social and emotional undercurrents, he notices subtleties Taki misses and shows care beyond his percussion section. He privately voices concern to Kumiko Oumae about Reina Kousaka's feelings towards Taki, accidentally revealing Taki's widowed status and ongoing grief in the process—a disclosure he later apologizes to Taki for.

Their deep college friendship involved constant mischief, with Hashimoto readily acknowledging Taki's greater popularity. After Taki's wife Chihiro died, Taki distanced himself, leaving Hashimoto feeling helpless and worried. Taki's invitation to teach at Kitauji reunites them; Hashimoto accepts with profound relief, nearly crying upon seeing Taki genuinely smile again after years of sadness. Their dynamic thrives on playful banter and inside jokes, like Hashimoto sneezing when Taki warns students about illness or their loud argument over ramen broth after nationals.

Assisting the band's national competition preparation, Hashimoto critiques Mizore Yoroizuka's playing as "robotic" and delivers a monologue urging the entire band toward expressive playing. He reassures students about performance orders and bolsters morale. Post-Kitauji's nationals performance, he celebrates by insisting Taki pay for their ramen.

His relationships include woodwind instructor Satomi Niiyama, a fellow college friend alongside Taki and Taki's then-girlfriend. The four formed a tight-knit group, viewing Niiyama as a younger sister figure.

Hashimoto's surname translates to "bridge" (橋) and "base/origin" (本). His given name Masahiro means "real/genuine" (真) and "command/esteem" (博). He prefers shio ramen.