The Fearsome Four of the Dark Duelling World is a gang of criminals founded and led by Mr. Heartland. They were revived by Vector to steal all numbers of Yuma Tsukumo, Reginald Kastle and kaito Tenjo.
At the beginning Erazor used his power to steal the memories of the citizens of Heartland city. Later he challenge in duel Yuma to take his numbers but Trey comes and helps Yuma in his duel against Erazor. Thanks to an excellent teamwork, they defeated Erazor and made him vanish.
After the defeat of Erazor , Mr. Heartland asks to Chironex to steal the numbers of Reginald Kastle. he infects his sister Rio with his poison to lure out Shark and stock him in his former house to infect him too, wagering the antidote on a Duel. Quattro arrives and helps Reginald in this duel, They won the duel together and made him vanish.
Mr Heartland sends Scritch to investigate Kite Tenjo. He discovers that Kite and Quinton can send Yuma into the Astral World. He infects Kaito with hallucinative poison and tries to prevent Kite and Quinton from sending Yuma off to the Astral World and initiated a Duel with the two. Even with the hallucinations of Kite, V and him defeated Scritch and make him vanish like Erazor and Chironex.
After the failures of Erazor, Chironex and Scritch, Vector gave to Mr. Heartland the number 1 which should enable his victory against Reginald and Kite. Kite Challenges him but the power of the number 1 caused him so much pain that he fell down. Yuma and Astral takes Kite's place and continue the duel for Kite, thanks to the ZEXAL power the duo won the duel. After the duel Heartland was incinerated by the fake numbers 1, 2, 3 and 4.