I don't even see why it's an issue. If Megaman has everything available to him in all games, then he would completely overwhelm Rikimaru. I'm going to guess there are 20+ Megaman games giving him 160+ weapons to choose from, four sub-tanks, and lots of upgrades(including body shield, life regeneration, effective double and triple jump, dog armor, fly armor, invul-to-spike armor, punch-down-walls armor, etc, etc, etc, etc, etc, etc). He has a beam sabre (which does half-life to any boss).

Due to the sheer amount of firepower, durability, and flexibility of Megaman, Rikimaru has no hope.

What is it they say about silence being golden?