2015 год. The sequel to the record-shattering Sonic the Hedgehog and Mega Man crossover is here! You saw what happened when "Worlds Collide!" Now brace yourself for when WORLDS UNITE! Dark forces have come together in the far future! The vicious conqueror Sigma has cheated death again and escaped the justice of X and the Maverick Hunters. He's crossed space and time to join forces with Zavok and the malicious Deadly Six of Lost Hex! Sonic and Mega Man could save us--but they've gone missing! Now the Freedom Fighters of Sonic's world and the Robot Masters of Mega Man's world must take up the fight to save their heroes and stop the coming tide of darkness! WORLDS UNITE features guest appearances by the cast of SONIC BOOM, MEGA MAN X and some of CAPCOM and SEGA's biggest stars!