Gudou no Kobushi

When martial artist Ikeuchi Mentaro is defeated in a tournament hosted by the Rokushin Kaikan karate school, he gives up karate to seek the strength he could not achieve through it. Soon enough, Rokushin Kaikan calls for another open tournament, and invites Ikeuchi and several other martial artists from different schools to compete. Ikeuchi sees this as the chance to get his revenge, and see how far he's come.

(Source: Kenganverse Fandom Wiki)