Countryside General

(from mangapedia):

Kaze Ozaemon, who lives in Aomori, is the strongest boy in his village, able to throw even a rampaging bear with his bare hands. Surrounded by animals, Ozaemon lives a peaceful life until one day he is suddenly visited by Yagoro Ohkaki, a close friend of his late father, Jinzaemon. He tells Ozaemon to come to Tokyo to fulfill a promise he made to Jinzaemon, but Ozaemon, who loves the village, refuses to go to Tokyo.

He challenges Ozaemon, who says he is the strongest man in the village and has never been beaten by anyone, to a match. Yagoro easily throws Ozaemon to the ground with judo techniques, and tells Ozaemon that he is a frog in a well, and encourages him to go out into the world and experience more things. Impressed by Yagoro's words, Ozaemon vows to become a superstar and decides to go to Tokyo.