Kōichi Tabuchi is a professional baseball player mirroring his real-life counterpart, fulfilling roles as catcher, first baseman, and cleanup hitter. The character uses the actual player's full name and team affiliation, interacting with real-world teammates Yasuda, Suzuki, Oh, and Hirooka, while his wife appears under the fictionalized name "Miyoko."

His narrative centers on exaggerated comedic situations from his baseball career, including being booed by spectators or facing peer ostracism. These portrayals incorporate contextual elements from the real player's life, such as performance slumps following a significant injury that led to hospitalization and weight gain, though the series never explicitly references these real circumstances as mitigating factors.

The real Kōichi Tabuchi endorsed this portrayal, appreciating its humor and crediting it with facilitating personal life events like meeting his spouse, affirming the character's role as a lighthearted caricature.

The character maintains a consistent persona across all adaptations: the original 1978–1979 manga, its 1985–1989 sequel series "Tabuchi-kun," and three theatrical anime films from 1979–1980. These depict no significant personal growth or background expansion, focusing instead on episodic comedic scenarios around baseball and interactions with other caricatured real-life figures in the sport. No additional backstory, personality evolution, or spin-off explorations beyond these appearances are documented.