Two iconic blue-clad video game protagonists with countless iterations that are arguably the mascot of certain video game companies (Capcom and Sega). Both of their main rivals are a mad scientist (Dr. Eggman and Dr. Wily) who have a large army of robots they constantly fight against, with one of these being their evil robotic counterparts (Bass and Metal Sonic). They also have crossed over a few times so that's something.

Idk if there are any connections besides that but it seems pretty decent

Classic Sonic by himself also technically works (especially since the Mega Man I'm using here is Classic Mega Man) but imo either work fine enough