On Earth, Tasuku Ryuenji, a young prodigy member of the Buddy Police, busts a fugitive in a Buddyfight as Gao Mikado watches the scene unfold on TV. On his way home, Gao saves a boy, Kiri Hyoryu, from a group of bullies using his Aiki-jūjutsu skills and returns home only to be scolded by his mother Suzumi. The next day, Gao goes to school, Aibo Academy, and meets up with his classmates: Kuguru Uki, Baku Omori, and Noboru Kodo. In class, he and his classmates open booster packs of Future Card Buddyfight when Gao suddenly pulls a Buddy Rare card, which summons Drum Bunker Dragon Fang Slade Terrestrial the 13th from the Dragon World. Drum's appearance means that Gao is to become buddies with him, although Drum is reluctant after having monitored Gao's actions from the Dragon World up to his point. Then, Tasuku and his buddy Jackknife Dragon arrive, and Tasuku gives Gao a Core Deck Case in recognition of him becoming buddies with a monster, officially making Gao a Buddyfighter. Tasuku takes his leave until Gao decides to challenge him to a Buddyfight.

Tasuku accepts Gao's sudden challenge, and the fight is arranged to take place later. During lunch, Gao gets help from Baku on building a deck to suit his playstyle. Then, Gao and Tasuku's Buddyfight commences in the school's amphitheatre as Gao's friends and little sister Hanako watch from the stands. Gao's aggressive strategy eventually earns him the victory over Tasuku, who then recognizes Gao as his rival and gives him the Gargantua Punisher card.

After Drum quickly gets comfortable living with Gao's family, Gao goes to school. He asks Baku to help reconstruct his deck to include the Gargantua Punisher card that he received from Tasuku, but Baku and Kuguru believe that Gao is not yet ready to use it and recommend him to find a "tuner" (training partner). Later, Gao meets the dancing and rapping Tetsuya Kurodake and wants him to be his tuner. Tetsuya agrees but only if Gao can beat him in a Buddyfight under special conditions. So, Gao battles Tetsuya, whose buddy turns out to be the popular entertainer Demon Lord, Asmodai. Nonetheless, Gao manages to win using Gargantua Punisher and becomes friends with Tetsuya after the fight.

Gao and Drum have an argument and get mad at each other as Gao goes to school (with Drum secretly following him). There, his class is introduced to a new transfer student: Kiri Hyoryu, who is the boy that Gao saved from the group of bullies and has since then admired Gao. After school, Gao takes Kiri to the Castle Store where the Manager teaches Kiri how to Buddyfight by having him play an actual game. Both Kiri and the Manager use trial decks to fight as Gao stays by Kiri's side. With helpful teaching from both Gao and the Manager and despite being new to the game, Kiri defeats the Manager. After the battle, Kiri is congratulated by a stranger, Rouga Aragami, who goes on to tell him that winning is most important. Gao expresses his disagreement with Rouga, who takes his leave. Then, the bullies appear to challenge Gao, who is reunited with Drum and beats one of the bullies in a Buddyfight. After the bullies retreat, Gao and Drum reconcile. Elsewhere, Rouga is instructed by his superior, Magoroku Shido, to retrieve photon metal. Rouga uses his Dark Core to assume the identity of "Wolf" and calls out his buddy Armorknight Cerberus to start the mission.

Gao's class is going to a field trip to the photon metal mines, but the trip is cancelled due to "Wolf" attacking the mines to steal Photon metal, however they don't realize the trip until they arrive.

Assuming his identity as the top Buddyfighter in 8th grade at Aibo Academy, Rouga challenges Gao to a Buddyfight, but Gao refuses. Rouga slips on a banana peel set up by Tetsuya and Asmodai , which prompts him to challenge Tetsuya, which Asmodai accepts (without Tetsuya's consent). During lunch break, while Rouga and Tetsuya battle, Gao is reminded about a time when he also believed that winning was everything like Rouga. When Gao's hunger for winning led to him injuring someone during a martial arts match, he realized that mentality is wrong. Gao has since then changed in order to make more friends.

Gao Mikado, wants to participate in the ABC Buddy Cup, but he needs to find a team first. Meanwhile, Noboru Kodo meets a mysterious old man.

Tasuku tries to convince his fellow Buddy Police members that Rouga is the criminal Wolf, but everyone says there is not enough evidence to prove it. Moreover, Commander I believes Wolf is not working alone and that Aibo Academy may be connected in the grand scheme of things. Meanwhile, at Aibo Academy, Magoroku, the school's student council president, and Sophia Sakharov, the vice-president, review all of the fighters who will be participating in the ABC Cup, including Gao, Tetsuya, Noboru (who recently became buddies with Dragon Knight, El Quixote), and especially Zanya Kisaragi, who was the only elementary student to have defeated the middle school students in the last ABC Cup.

To conquer Gao Mikado's weakness, both Baku Omori and Kuguru Uki suggest him to construct a new deck. However, Gao disagrees with the idea. At the same time, Jin Magatsu from the middle school stole Gao's deck!

Noboru goes to the Buddy Police headquarters to void his contract with El Quixote and be done with Buddyfighting. Suddenly, the alarm sounds due to the appearance of the criminal Akaoni Kanme, prompting Tasuku and Takihara to apprehend him. Noboru is invited by Commander I into the Buddy Police's main room where he not only watches Tasuku defeat and arrest Akaoni, but he also learns about Tasuku's past. Noboru then runs off, frustrated at himself for not being special like Tasuku or Gao. Nonetheless, he gets encouragement from El Quixote who tells him to do what he wants to do, regardless of what others may say.

One of the grade 7 students, Suzuha Amanosuzu and her buddy, Center of the World, Mary Sue. It is said no miracle shall happened before her.

Round 2 of the ABC Cup, it's the buddyfight between Zanya Kisaragi and the team Discipline Committee but the buddyfighter has gone missing.

Shido tries to collude with Jin to defeat all opponents in the ABC Cup and let Shido win the entire tournament. However, Jin declines after Shido refuses to offer more compensation to him. When Jin leaves, he starts thinking of purposely losing his upcoming fight against Tetsuya. Tasuku, who is on an undercover mission, overhears Jin and chastises him. Then, continuing his mission, Tasuku and Jackknife Dragon find their target, a dark monster named Azi Dahaka (the same monster in charge of Shido). Azi Dahaka takes Tasuku and Jackknife to a battle arena in a different dimension where they are confronted by Superarmor Dragon, Galvanic Feather Dragon. Back on Earth, the ABC Cup continues as Jin plays against Tetsuya. Although still intending to lose the match, Jin is suddenly reminded of Gao, which motivates him to defeat Tetsuya and advance in the Cup. In the other dimension, Tasuku and Jackknife try to fight together against Galvanic Feather Dragon, who fends them off easily. Reminded of the time in which they combined their powers to create the Gargantua Punisher card, Tasuku and Jackknife do the same thing again to make a new card, Dragonic Punisher, to defeat Galvanic Feather Dragon. After Galvanic Feather Dragon decides to join Tasuku and Jackknife, they safely return to Earth, where Tasuku congratulates Jin on his victory and apologizes to him.

The next quarterfinal match of the ABC Cup will be Noboru versus Shido. Before the match begins, Noboru meets with Shido in the student council room, where it is revealed that Noboru had unwittingly been bribed by Shido to lose to him during the previous ABC Cup. However, he decides to not take his bribe this time but still intends to throw the match. With helpful advice from El Quixote, Noboru resolves himself to not only have a fair fight against Shido but also reconstruct his deck to include a certain card.

Gao and his friends are informed by Noboru's parents that they and Noboru will leave the country soon. Then, the first semifinal match of the ABC Cup commences with Gao facing Noboru. While fighting, in addition to recalling their pasts, Gao is infuriated that Noboru did not tell anyone about his departure, while Noboru expresses his frustration over how Gao always seems to be in the spotlight. Despite Noboru following advice from the teammates (Maihama and Niitani) he ignored, Gao emerges victorious. Afterwards, at an airport, Gao and his friends bid farewell to Noboru, who sheds tears and subsequently leaves Japan.

Gao and his friends learn from the Seifukai that Doai is missing. They also learn that Zanya knows something about it and has found Genma's deck in the student council office. However, the deck is currently in the possession of Zanya's little brother, Akatsuki, who wants to give the deck back to Seifukai but is nowhere to be found. So, while Zanya fights against Jin in the last semifinal match of the ABC Cup, Gao and the rest try to search for Akatsuki. Sophia locates and gets to Akatsuki first, and she then takes him to the student council office. Gao and company track them down but see Akatsuki returning to Zanya, who defeats Jin. Afterwards, everyone regroups, and Akatsuki gives the box containing Genma's deck back to Seifukai, but everyone is shocked when they discover the box is empty. Back at the student council room, it is revealed that Sophia has taken the deck...

Intending to have Genma inherit the Dark Core (which was formerly in Rouga's possession), Sophia uses the Dark Core on Doai. She puts Doai under her control and has him attack Genma to coerce him into using the Core. Meanwhile, Gao, his friends, and family members are having a dinner party when Akatsuki drops in. Zanya arrives to retrieve him while also telling Gao that he does not see him as a rival.

Genma and Magoroku have their Buddyfight with both of them using Ancient World decks. As the fight goes on, Genma expresses his disgust at how Magoroku is acting as student council president. He also shares his ideals of how the president should be like the "sun", which intrigues Gao. Genma eventually uses his powerful buddy monster Martial Arts Dragon Emperor, Duel Sieger to defeat Magoroku.

After Genma defeats Zanya, the tournament is temporarily put on hold to repair the fight stadium. Gao and his friends meet at his home, and then Doai appears to deliver a message from Genma, telling Gao to withdraw from the upcoming match. Gao refuses to do so, which Doai expected, and before leaving, he warns Gao about Genma's Koryukien deck. Later, while Gao and his friends are having a dinner party, Suzumi reminisces about Gao's deceased older brother Yota and talks about how she wanted to keep Gao close to her. She then resolves her feelings and gives Gao a card that Yota left behind, which Gao decides to add to his deck. The next day, the final Buddyfight in the ABC Cup between Gao and Genma ensues.

Just when Gao defeats Duel Sieger "Spartand", Genma evolves it into its ultimate form: Duel Sieger "Tempest Enforcer". After attacking Gao with "Tempest Enforcer" three times, Genma reveals that he was once friends with Gao's brother Yota. They met while in the hospital where a young Genma became interested in Yota's comics about the "Mighty Sun Fighter". Genma was inspired by the message of the Sun Fighter, thinking it meant to be a strong leader for others to follow, which shaped him to the person he currently is and claiming the title of "Mighty Sun Fighter" to himself. However, Gao refutes him by saying the real purpose of the Sun Fighter is to serve as a role model to motivate others to follow their dreams. As Genma realizes his misunderstanding, Gao uses the card that Yota left (which is revealed to have originally belonged to Genma): Sun Fist, Sunshine Impact. Attacking together with Drum Bunker Dragon, Gao destroys "Tempest Enforcer", which, due to its negative effect, causes Genma to instantly lose, thus making Gao and Team Balle du Soleil the winners of the ABC Cup. In celebration of this victory, Gao and his friends have a party and are later joined by Genma, who gives Yota's comics to Gao and pays his respects to Yota. Despite the cheery atmosphere, Drum is feeling unsatisfied with his overall performance and tries to think of ways to become stronger...

Gao and his friends gather in his home where they recap and discuss the events of the ABC Cup. Meanwhile, the Buddy Police is taken over by Sueroku, who is Magoroku Shido's father and also a special detective. Because of Tasuku's unauthorized usage of Future Force, Sueroku forbids him from using Buddyfight cards for one month. Elsewhere, Sophia has a meeting with her master, Kyoya Gaen. Later, after Gao's family visits Yota's grave, Suzumi tells Gao that she has taken a job to teach martial arts in North America. Although initially shocked, Gao and the rest become supportive of Suzumi's decision.

Gao, Tasuku, and the other participants of the ABC Cup are invited on a cruise ship party hosted by Kyoya Gaen, who is working with Sophia to look for a candidate Buddyfighter to use the Dark Core and Disaster Force. Later, Kyoya tries to present a special rare card to be given to a Buddyfighter of his choosing, but it goes missing. Although it seemed as if the card was stolen, it turns out that the card was in fact the monster Dragowizard, Qinus Axia who had gone off on his own because he did not want to be given away.

Drum returns to Dragon World to seek advice on becoming stronger from his father. He asks Drum if strength is all Drum wants and then kicks him into Dungeon World, where Drum gets equipped with a new weapon and armor. He saves a village by inadvertently slaying a rampaging golem monster. The villagers (who look similar to Gao's human friends from Earth) then believe that Drum is a legendary hero and request him to defeat the king of the monsters in the mountains. After being given a stone tablet that is reminiscent of a Buddyfight deck, Drum uses it to summon other heroes who closely resemble Tasuku, Baku, Kuguru, and Tetsuya to aid in his quest. Although the group was initially disorganized, Drum eventually realizes that working together and not giving up are keys to getting stronger. He finishes the quest and reports back to his father, who then kicks Drum into another world for more training.

Gao and Kazane engage in a Buddyfight, in which Kazane exhibits more of the fun gambling style of her Dungeon World deck. With Drum returning to Gao's side to aid him in battle, Gao defeats Kazane, and the two fighters become friends. Elsewhere, Kiri is feeling pessimistic about his Buddyfighting skills when Rouga suddenly appears and takes him away. Having witnessed this scene, Paruko Nanana informs Gao and the rest about Kiri's abduction. They later learn that Kiri has been taken to Sengoku Academy...

Borrowing Suzuha's airship, Gao and his friends travel to Sengoku Academy, a supremacist school in the mountains where everything is resolved through Buddyfights. On the way there, the group is attacked by the monster Sky Ninja, Yamigarasu but saved by the timely appearances of Genma and Duel Sieger. The team lands within Sengoku Academy and are challenged by several Sengoku students. Gao and his friends beat them all in Buddyfights, and they are later given a tour of the school by Shosetsu Kirisame, who is one of the "four demon generals" of Sengoku Academy. After meeting with the other three generals (Raremaro, Kanahebi, and Kemura), Rouga appears and Gao demands to know where Kiri is. Then, Rouga has Gao and his band of friends engage in a 5-vs-5 Waseda style of Buddyfight with Rouga teaming with the four generals. In the first match, Tetsuya and Rouga face off. Tetsuya tries to win the fight in the first turn, but Rouga retaliates with new cards to quickly finish the battle in the following turn. Gao angrily watches as Rouga demands for someone stronger to step up...