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Based on Ishii Hisaichi's 1979 manga Ganbare!! Tabuchi-kun!!, serialized in weekly Manga Action magazine.

The Seibu Lions baseball team makes it to the next round of a baseball tournament thanks to the heroic efforts of its star player, Tabuchi, but the next stage will involve hard work and cooperation. In a sports anime that pitches caricatures of real-life players against cartoon characters, the Lions (whose real-life mascot is the grown-up Kimba the White Lion), keep losing games due to Tabuchi's poor condition-his shadow is getting paler.
A group of fellow players turns up at the stadium, accompanied by Dokaben, and they encourage Tabuchi to pull through. They organize a Tabuchi Day to show him how appreciated he is, but it is a miserable failure.
Eventually, he is brought out of his depression by the arrival of a girl called Miyoko, who obliges by dressing up as a cheerleader.

Note: Real-life members of the Seibu Lions baseball team are caricatured.

(Source: AniDB)