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The ten parallel realms connected to Earth are known as Worlds. And at long last, the time to decide the World’s Number One has come! Gao Mikado, a sixth-grader from Aibo Academy elementary division, has been chosen to represent Dragon World in the World Buddy Masters tournament. Guided by a messenger who claimed to be Saint Holy Sword Dragon, Gao went to Dragon World itself in search of his new Buddy! As if that was not an adventure enough, Gao interfered with the seal on an ancient shrine and released a forbidden monster! Known as the Demon Lord Dragon, Batzz, this forbidden monster had once devastated the continent of Dragon World. Batzz is a tyrannical monster which pays no heed to anyone. Yet, Gao believes he can become Buddies with even such a monster, and entered the tournament with him. Ten representatives from ten Worlds. One legendary Mirage Card that is bestowed to the winner. An organization plotting for the legendary card, led by a man called Wisdom. What will Gao, and his new buddy, Batzz get themselves into this time!?
Gao Mikado, a 6th year student of the Aibo Academy Elementary Division, is partnered with Dragon of the Sun, Bal Dragon, a monster born from a mysterious egg. To earn the coveted title as the strongest fighter in the world, Gao and Bal team up to challenge other fighters in the "World Buddy Cup". The two will have to battle others in a card game called Buddyfight, which allows monsters to fight alongside humans as buddies. Their rivals include ex-Buddy Police Tasuku Ryuenji, and the self-proclaimed strongest combination, Gaito Kurouzu and his buddy monster Black Death Dragon, Abygale.
While Tasuku is off training and getting rest in the world of the monsters, the Buddy Police sees the need to deputize some of the champions to help protect the Earth. Gao, Tetsuya, and Zanya Kisaragi are among those deputized, and it's just in time. A new enemy arrives, Ikazuchi, with the deadly 100 demons, all rogue monsters. Now the new trainees and the Great 8 monsters must fight to protect Earth from being consumed by these new rogues.
Humans intermingle with beings from the parallel world of "Shinkinkai." The "Buddyfight" game chooses humans ("Buddyfighters") and partners them with Buddy Monsters from Shinkinkai, and the duo fight against other Buddyfighters. The battles in these games can sometimes even influence the fate of nations. Gaō Mikado is a sixth-year student at the "Aibo Academy" elementary division who longs to be a Buddyfighter and to be partnered with a Monster. One day Gaō notices a young boy being bullied by delinquents, and he helps him out using his Aiki-jujutsu skills. Drum Bunker Dragon, a Monster and the son of the hero of Dragon World, watches Gaō's actions, and decides to form a pact with him as his buddy.
In the world of Duel Monsters, the Blue-Eyes White Dragon brings victory, but the Red-Eyes Black Dragon brings possibility. Shyoga has never been good at Duel Monsters, always losing every game he’s played - that is, until the day he pulls the legendary Red-Eyes Black Dragon out of a booster pack. With such a rare card under his belt, Shyoga is convinced that he would be undefeatable and refuses to battle a single opponent. But when Kaiba Seto is drawn to Shyoga and his card, Shyoga finds himself forced into a tournament with Mutou Yugi at his side. Now, Shyoga must find the courage to fight, but what possibility can a single Red-Eyes bring when staring down three Blue-Eyes? Will Shyoga lose his precious card due to his cowardice, or will Kaiba reclaim his position as the number one duelist?