MegaMan's fiercest enemy Bass has returned and he's more powerful than ever. Vested by the Dark Power, Bass has fused with CyberBeast Grave to become DenTech City's worst nightmare.

To save the day, MegaMan and ProtoMan must come together using the SoulUnion program. Apart, the two friends are no match for the new Bass. But together, there's a chance they can smash their archenemy to smithereens.