Gohei Ōji is the husband of Michiko Ōji and the father of Mochizō Ōji, and he operates the Ōji-ya mochi shop. Physically, he is a man in his early thirties with hair that falls behind his ears, a slight mustache, and eyes that are never depicted as fully open. His typical attire consists of t-shirts printed with English phrases paired with jeans.

In terms of personality, Gohei is characterized as a laidback individual with a preference for modern tastes, which often contrasts with the more traditional views of his neighbor and rival, Mamedai Kitashirakawa. Unlike the shopkeeper across the street who views Mochizō as a spy, Gohei is welcoming and on friendly terms with Tamako Kitashirakawa. He enjoys incorporating English into his business, having re-named his shop Ōji-ya Ricecake Oh! Zee, and he created a product called Love You Forever mochi. Despite his generally relaxed demeanor, he can react in a childish manner, such as when he learned of his son's decision to move to Tokyo to study film; he turned his head dramatically and gave Mochizō the silent treatment, later venting his worries at a bar with Mamedai.

Gohei's primary motivation and role in the story revolve around his family business and his relationship with his son. His frustration over Mochizō's departure for university underscores a deep, if not openly expressed, love for his son. His key relationships include a contentious yet familiar bond with Mamedai Kitashirakawa. The two often argue over their contrasting philosophies on mochi-making, with Mamedai being the traditionalist. These disagreements can occasionally escalate into minor physical fights, yet despite this, Mamedai has acknowledged that they frequently go out drinking together. Gohei does not demonstrate any notable abilities beyond those associated with running a traditional mochi shop and his distinctive approach to modernizing its image.