>>28731809I was the guy who first made this image, but I've seen other people post it around. I'm trying not to copy-paste my explanation every time, since I know that's the quickest way to piss people off, but it's surprising how direct the inspiration is from Ashita no Joe to Lycanroc.
I would highly recommend the series. If you want to watch it, there's a live action film which covers the first half of the show, and the anime can be picked up from Ashita no Joe 2. You could also just read the series, but I appreciated the sound and music direction with the show, especially with the melancholic second half.