The Mysterious Deadly Boxer: Mirror X?

Inazuman – Season 1

Goro's childhood friend, former pro boxer Ryu, wants his younger brother Masaru to become a world champion. He needs money to build a gym where his brother can train. He enters a match against Mirror X for a five-million-yen purse and is gravely injured. Now Masaru must fight in order to earn enough money for his brother's surgery…