Sei Iori is a Gunpla builder whose family runs a hobby shop in a small town. He aspires to be a Gunpla Battle champion like his father, but despite his exceptional building skills, he lacks the combat abilities to compete with other contestants. Then one day, he meets a mysterious boy named Reiji, who helps him improve his confidence in participating in Gunpla Battles. Together, Sei and Reiji battle their way to the 7th Gunpla Battle World Tournament.
Episode 1
Sei Iori is a talented Gunpla builder, but lacks the confidence to become an effective fighter in a Gunpla Battle. One day, he meets Reiji, a mysterious red-haired boy, who displays his exceptional skills as a Gunpla Fighter by defeating Susumu Sazaki with Sei's newly constructed Build Strike Gundam.
Episode 2
As Reiji copes with adjusting to Tokyo life, he picks a fight with school council member Monta Gonda. Sei and Reiji defeat Gonda in an exhibition Gunpla Battle, but are immediately bested by Tatsuya Yuuki and his Zaku Amazing.
Episode 3
Sei completes an upgrade to the Build Strike Gundam while Mr. Ral gives Reiji an orientation on Gunpla Battle.
Episode 4
Sei falls in love with a mysterious girl who is into Gunpla, unaware of her true intentions in Gunpla Battle.
Episode 5
Sei and China meet Mao Yasaka, a young Gunpla Fighter from Kansai Prefecture.
Episode 6
When Yuuki suddenly bows out of competition and takes an indefinite leave from school, Reiji begins to doubt his purpose in Gunpla Battle.
Episode 7
As a reward for winning the Gunpla Battle Japan 3rd Block Championship, Sei and Reiji, along with China, Rinko, and Mr. Ral, take a vacation at a beachfront inn. But their vacation is cut short by a former Gunpla Builder who threatens the innkeeper to give him their property.
Episode 8
Nils Nielsen, a 13-year-old genius, joins the American Qualifying Round of the World Championship to learn more about the secrets of Plavsky particles. Meanwhile, in Finland, Team Nemesis receives a new fighter named Aila Jyrkiainen from the Flana Institute.
Episode 9
China completes her Gunpla Beargguy III (San), and when a painting of it wins the grand prize at the local art exhibit, her rival Caroline Yajima issues her a Gunpla challenge.
Episode 10
As the 7th Gunpla Battle World Championships begins in Shizuoka, the Gunpla community is in shock when news spreads of reigning champion Carlos Kaiser's defeat at the hands of Aila. Meanwhile, Sei meets the other Gunpla Fighters at the opening party while Reiji encounters Aila at the nearby mall.
Episode 11
Yuuki makes his World Championship debut as PPSE's Meijin Kawaguchi. Meanwhile, on the second day of the tournament, all of the participants must face each other in a battle royal until only one-third of the lineup remains.
Episode 12
With an unmanned Mega Size Model Zaku sent in to eliminate the Star Build Strike Gundam in the middle of the battle royal, unlikely alliances are formed while Sei and Reiji must unleash Star Build Strike Gundam's trump card to survive.
Episode 13
For day three of the tournament, containers with random weapons are placed in the battlefield for the Gunpla Fighters to use in their battle; each contestant is assigned a container number to use. Sei and Reiji are assigned to battle Luang Dallara, who already gave them trouble at the battle royal. Worsening the situation is Reiji's wrist injury from a street fight outside the arena grounds.
Episode 14
Sei and Reiji remain undefeated by the sixth period of the tournament with two more to go, despite Reiji's wrist injury. However, another obstacle appears in front of them in the form of the Gunpla Fighter named "C".
Episode 15
With their loss in the Gunpla race dropping them to 17th place, Sei and Reiji must leave no room for error in the eighth period of the tournament in order to make it to the finals. However, they have to go through Fellini in the process.
Episode 16
As Rinko leaves home to join her son, Sei and Reiji's battle with Fellini ends in a draw, but they earn two points, which is enough to land them in the top 16 in the finals. Meanwhile, following a heated argument with Sei over rebuilding the Star Build Strike Gundam, Reiji goes out to buy his own Gunpla, only for him and Aila to receive a crash course in Gunpla building by a mysterious bearded man.
Episode 17
On the first day of the tournament finals, Mao is scheduled to battle Sei and Reiji. But when he cannot think of a strategy to defeat the Star Build Strike Gundam, he returns to his mentor, Master Chinan, and asks him to teach him the master's ultimate technique.
Episode 18
After shocking the Gunpla world by defeating Luang on the first round, the Renato Brothers and their GM Sniper K9 set their sights on Meijin Kawaguchi.
Episode 19
Sei and Reiji must go through Nils in order to continue their quest for the championship. Desperate to prevent the duo from advancing, Baker offers to have PPSE sponsor Nils, but knowing very well not to trust her, he arranges for a secret meeting with Sei and Reiji to extract the secrets of Plavsky particles from them.
Episode 20
Fellini faces Aila in the quarterfinals, much to Sei and Reiji's shock as they finally discover her real identity. Aila is pressured to win the championship due to the arrival of the Team Nemesis Chairman, who has promised the trophy to his grandson for his birthday.
Episode 21
Following Aila's revelation as a Gunpla Fighter, an angry Reiji vows to defeat her in the tournament.
Episode 22
Yuuki must prove himself worthy of the name "Meijin Kawaguchi the 3rd" when he battles Julian Ayers Mackenzie, a British Gunpla Fighter who was to have taken that title three years prior.
Episode 23
A festival is held in Shizuoka one week before the final round of the tournament, where guests can participate in Free Battle rounds against the championship's competitors. Meanwhile, Nils and Caroline follow a truck that leads them to the source of Plavsky particles.
Episode 24
In the final round of the tournament, Meijin Kawaguchi the 3rd unveils the true form of his Gundam Amazing Exia. However, he brings forth a disturbing aura in the arena reminiscent of his predecessor.
Episode 25
Sei and Reiji's victory in the tournament causes Chairman Mashita to panic, with his Arista resonating all Plavsky particles in the PPSE Stadium to form a 1/144 scale replica of the Zeon space fortress A Baoa Qu over the facility. The Gunpla Fighters must band together to break into the fortress and destroy the Arista before it produces disastrous results.
