Ashita no Joe 2

Before Hajime no Ippo there was Ashita no Joe, same theme about boxing and only boxing. If you like Hajime no Ippo you will most likely love Ashita no Joe season 1 and 2. 

Protagonists that will do whatever it takes to quench their thirst for what they want most (for Spike, revenge. for Joe, the fire of the ring), even if it could mean the end of them. Also has tons of characters with complicated relationships who aren't honest about themselves. Both are two of the best things ever made. 

Although prominently featuring an activity, such as the refinement of advanced technology in Texhnolyze, or the sport of boxing in Ashita no Joe, each show accompanies its protagonist alongside their involvement in these interests. They start in an almost animal state, to a refined master of their craft. They change and evolve with the revelations made about each subject as well, finding an end to these journeys in a certain comforting, bittersweet appreciation of fleeting life. 

The central theme, boxing, and a lot of inspiration 

Both are very similar but eventually off in different directions. Both are tales of redemption and dealing with PTSD and trauma. Both are beautiful stories about a guy named Joe. 

I would say these are both masterpieces. They have character driven stories and are so heartwarming. Interesting characters and themes 

Both deal with trauma, guilt, PTSD in interesting ways. And both Thorfinn and Joe have some of the best character development in all of fiction.