Joe del mañana (1968)

15 year old Joe Yabuki is a wondering orphan who stumbles across the worst slumps of Tokyo. There, he encounters a washed up boxer who wants to train Joe after he easily beats up some yakuza. However, Joe does not take the trainer, Tange, very seriously until they end up in jail for fighting the yakuza in the park. Joe then decides to live with Tange but does not show any appreciation to him at all. He then uses the neighborhood children to fake an orphanage fund and get money. Joe is then exposed and is forced 13 months of juvie. While in juvie, he meets a boxer impronsed for assault, Rikiishi Tooru, while making an escape. Rikiishi stops Joe’s plan and it starts a rivalry that inspires Joe to take boxing not as a means to get revenge against Rikiishi, but to reform his life and pursue as a career.

Source: www.anisearch.com/manga/1930