MÄR, Katekyo Hitman Reborn! Recommendations
They both have a lot of fighting and the characters improve their abilities throughout the series. They also get their powers from jewelry/objects (khr has rings while MAR has other jewelry). The main protagonists personalities are different but what they fight for is very similar.
They are both on fighting with special powers against specific opponents.... and when they have their fights, they have one-on-one matches to see who wins... (Even though i do think that KHR is better.... no offence)
both have the main character being the strongest (except for specific characters) and get specific training which gave the extra improvements....
both great animes!!