Fighting games that dont require combinations of inputs?
Divekick probably thr most simple fighting game out there that only requires 2 buttons to play, which is the jump & kick button. There's also the old Digimon Rumble Arena/Rumble Arena 2 that was also very simple to play, and wasn't hard to play. Dengeki Bunko Fighting Climax/Ignition also has a very easy one-button full combo + special move, which was specially designed for newcomers. Gundam Versus also has a pretty straightforward movelist, but it's a 2v2 team fighting game instead of the traditional 1v1. In reality, there's only a few fighting games that were casual friendly. The best you can get is the game provides a simple "one button auto combo" for newcomers, but you still need to know the other moves in order to play effectively.