Having transferred to the Seiho Academy, Sekai discovers that he and Yuuma are in the same class. He challenges Yuuma to a battle but is bluntly rejected. Meanwhile, the school's student council has decided to merge the Gunpla Battle Club with the Plastic Model Club. To survive on its own, the Battle Club must defeat the Plamo Club in battle, and Yuuma is among the latter's players. With the Battle Club facing three-to-two odds, the battle seems like a mere formality, but Fumina's tactics let them put up a good fight. Miyaga loses his temper and deploys the huge mobile armor Agrissa, finally backing Fumina into a corner. But Yuuma, unable to accept that his club president is trying to win by ignoring the previously agreed rules, teams up with Sekai to destroy Miyaga's Agrissa. Thus, with the addition of Yuuma, team Try Fighters is finally formed!

Having achieved their first victory in the practice match with Gyanko, the Try Fighters are training hard for the regional qualifiers which will be held in one month. Fumina is thinking of building a new mobile suit for use in the tournament, and when she confers with Mr. Ral, he suggests that she and Sekai take a trip to G-Muse. Here, Fumina virtually goes into a trance as she tries to choose a Gunpla, and Sekai is soon bored of watching her. A clerk encourages Sekai to build his first Gunpla, the Musha Godmaru, which he uses to battle some little kids. As Fumina rejoins him, they encounter Minato Sakai, a middle-school builder from Osaka. In the twinkling of an eye, Minato builds his own Kouki Gundam and begins a battle with Sekai. Thanks to his knowledge of SD Gundams' unique traits, Minato gives Sekai a hard fight and ultimately defeats him. But this battle has given Sekai and Fumina some valuable ideas for the tournament.

Through the battle with Minato Sakai, Sekai and Fumina have realized what they need to do, and they quickly begin working towards the championship. Meanwhile, in order to keep his promise to Fumina, Yuuma is building power-up equipment for his Lightning Gundam. But rival teams are also steadily preparing for the regional qualifying tournament. Each with their own dreams in their hearts, they all gather for the Gunpla Battle Japanese Under-19 Championship’s West Tokyo Tournament. On the first day of the tournament, Fumina arrives with her just-completed Winning Gundam, and Sekai and Yuuma have been making their own preparations too. A random drawing determines that the Try Fighters will fight in match three of the first day. Demonstrating the results of all their efforts thus far, the Try Fighters finally begin their struggle to reach the national tournament!

The Try Fighters have achieved a splendid victory in the first round of the regional qualifiers, and they celebrate with a modest toast. But their joy is short-lived as they learn who they will face in round two. Their opponent is Seiren Technical College, a veteran team which is favored to win the championship. Whatever tactics their foes try, Seiren anticipates their moves and drives them to defeat, and thus it’s said that this team rules the battlefield. The night before the match, Fumina summons Sekai and Yuuma to the club room, where they witness a hidden feature of the Winning Gundam which may be their ace in the hole. The Try Fighters face the second round with perfect poise, but Seiren’s three Ez-SR units have analyzed the characteristics of the fighters as well as their machines, and now they strike precisely at the Try Fighters’ weakest points!

After defeating the veterans of Seiren Technical College, the Try Fighters win an easy victory in the third round, as their opponents self-destruct! They are advancing to the quarterfinals! Fumina and the others observe the following match to see their next opponent, Joto Middle School. After the match, two members of the Joto Middle School team beg the Try Fighters to let them win for the sake of their team leader Shimon Izuna’s little brother Mamoru, who is battling a serious illness. Fumina and the others are bewildered by this unexpected request, and begin to question their own reasons for fighting. In order to see the situation for himself and test his resolve, Sekai goes alone to the hospital where Shimon’s brother is being treated. Here, Sekai issues a straightforward declaration of war to Mamoru the Gunpla builder, and to his opponent Shimon!

The Try Fighters have made it into the semifinals as one of the best four teams. A drawing is held to determine the brackets, and they are matched up with Suiryu Academy. Meanwhile, Gyanko’s team from St. Odessa Girls’ School will face last year’s regional champion, the Miyazato Institute. As if from the pressure of fighting the previous champion school, Gyanko comes crying to Sekai before the battle. Out of compassion, Fumina leaves Gyanko alone with Sekai at a fast food restaurant, but it turns out that Gyanko is just playing on Sekai’s sympathy to make him agree to a date. Despite her meek behavior, Gyanko’s strategy fails when Sekai realizes her intentions. Then they suddenly run into Yomi Sakashita and Akira Suga from the Miyazato Institute, and Suga declares that Sekai’s Jigen Haoh school of kenpo won’t work on him. As they go to face their respective semifinals opponents, Gyanko and Sekai promise each other that they’ll meet in the final round…

The Try Fighters' opponent in the final round will be last year's regional champion, team G-Master from the Miyazato Institute. The two teams prepare for the final battle, each with their own resolve and desires. The battlefield for the final match is the space fortress Solomon. Outside the fortress, Yuuma's Lightning Gundam exchanges fire with Sudou, who is using the Mega-Shiki built by Minato Sakai of the Shingyo school. Meanwhile, Sekai and Fumina begin a battle inside the fortress with Suga and Sakashita, who were already lying in wait for them. As the fierce fighting continues, Sekai and Fumina exit the fortress. Sudou attempts to shoot them down with his high mega particle cannon, but Yuuma stops him as they trade simultaneous blows. Battered and broken, Sekai and Suga cling to the hope of victory, clashing in a final desperate effort.

Now that their end-of-term exams are over, the Try Fighters are going to a training camp to prepare for the national tournament which will take place during summer vacation. Mr. Ral has kindly arranged for them to visit the Nielsen Labs, a facility equipped with the industry's leading battle environment, where all the regular national tournament teams gather. There, Sekai and his comrades end up agreeing to a practice match against team White Wolf from the Gabai Institute, the representatives from Kagoshima, who were using the battle system for a mock battle. Thanks to Sekai, however, the Try Fighters arrive later than planned and find that in the meantime the White Wolf members have been wiped out by a single Gunpla. When Yuuma sees this Gunpla, he abruptly intervenes and challenges it to battle. Fumina and the others are bewildered by Yuuma's unexpected action, but it was this same Gunpla that drove Yuuma away from Gunpla Battle two years earlier.

The Try Fighters have been utterly defeated by Gundam The End, the Gunpla controlled by Saga Adou of the Gunpla Academy. Yuuma is unable to hide his shock at witnessing the vast difference in their abilities, and he flees the scene, leaving his teammates behind. The concerned Fumina asks Mr. Ral to look after Sekai, who has collapsed as a result of assimilation, while she goes in search of Yuuma. Meanwhile, Meijin Kawaguchi appears before the dispirited Yuuma. Without explanation, the Meijin spirits him away in his motorcycle sidecar. Fumina sees them go, and is then approached by Lady Kawaguchi, who warns her that "As a Gunpla builder and fighter, you're definitely lacking something." To restore their lost confidence, and show them what they lack, the two Kawaguchis challenge Yuuma and Fumina to battle!

Having recovered from his battle with Adou, Sekai heads for the Labs' workshop to repair the Build Burning Gundam, and encounters a mysterious girl. Thanks to the girl's advice, Sekai finishes repairing the Build Burning, and the next day he goes to the Labs' battle room with Mr. Ral for special training. There he meets Kei Karima from Honmoku Academy, representing Kanagawa, who suggests they play a practice match. His goal is to learn the strength of the Gunpla Academy, and when Sekai realizes this, he cannot hide his anger. At this point Wilfrid Kijima, the ace of the Gunpla Academy, intervenes, as does the Gabai Institute team that represents Kagoshima. It seems the situation will get out of hand, until Meijin Kawaguchi suddenly appears on top of the battle system. Thus begins a Battle Royal among representatives of each school, under the Meijin's supervision.

During a Battle Royal among representatives from each school under the Meijin's supervision, Sekai Kamiki and Wilfrid Kijima have acknowledged each other as rivals, and they promise to fight again at the national tournament. Yuuma Kousaka, meanwhile, declares that he will get revenge on Saga Adou and looks to the tournament with fresh resolve. Elsewhere, the final regional qualifiers are completed, after being delayed by problems with the venue. The winner of the Osaka qualifiers is team Build Busters from Tendaiji Academy, to which Minato Sakai now belongs. With the national tournament 10 days away, the champions from the participating schools steadily make their preparations. Fumina and her comrades, aiming to defeat the Gunpla Academy, set out to power up their own Gunpla and address their shortcomings based on their experiences at the Nielsen Labs. As the start of the tournament draws near, Gyanko and others come to help, and at last the Try Fighters' new machines are completed.

Once upon a time, the Gunpla Battle world championship was held at the PPSE Stadium. After the Plavsky particle accident seven years ago, the damaged stadium was demolished, and a monument was placed there bearing the names of previous champions. Now, the Gunpla Battle Japanese Championship tournament is about to begin at the Yajima Stadium, which has been newly constructed next to this site. As champions gather from every prefecture, having fought their way through the regional qualifiers, Sekai again encounters Wilfrid Kijima of the Gunpla Academy. Meanwhile, Yuuma learns that Minato Sakai is also entering the tournament as one of the representatives from Osaka. The next day, brackets are drawn after the opening ceremonies, and the Try Fighters immediately enter battle as they are assigned the first match of the tournament. Their opponent is Okhotsk Academy, representing South Hokkaido, a team that placed in the best 8 of last year’s national tournament!

Minato Sakai and his teammates from Tendaiji Academy, representing Osaka, easily make it through the first round of the tournament thanks to the overwhelming power of their unique Gunpla, the Tryon 3. Other rivals that Sekai and his comrades met at the Nielsen Labs, such as the Gabai Institute from Kagoshima and the Toritsu Academy from Niigata, likewise survive the first round. As the tournament enters its second round, the top-seeded Gunpla Academy finally enters battle. The Gunpla Academy’s third fighter is Shia Kijima, the girl who taught Sekai how to repair the Build Burning. The attention of the whole venue is focused on the Gunpla Academy as it battles Honmoku Academy, representing Kanagawa. But its team leader, Wilfrid Kijima, orders Shia to sortie alone as a penalty for waiting until the very last minute to complete her Gunpla. Now Shia’s G-Portent must confront Honmoku Academy on its own.

In the second round of the tournament, the Try Fighters will be facing team SD-R from Toritsu Academy, representing Niigata. These three brothers are formidable enemies, who have made it this far by thoroughly analyzing their opponents' data, and then using their SD Gundams to execute precision tactics with skillful teamwork. As rival players look on, the battle finally begins. The Try Fighters must search through a huge haunted castle, watching out for enemy attacks. But due to Yuuma's unexpected weak point, they fall for their opponent's plan, and the Try Fighters are split up. Fumina heads underground to rejoin her teammates, and finds that a time bomb has been planted to block her path. Meanwhile, Sekai and Yuuma have fallen underground and are now in peril due to the enemy's Absorb System, which pins down their machines by absorbing Plavsky particles.

The Try Fighters have been cornered by the Snibal-Drago-Gira which Toshiya Shiki created out of his grudge towards the Gunpla Academy. This monster now threatens them with its clever tactics, and the firepower it has gained by stealing their own particles with its Absorb System. Even as he endures the enemy's fierce attack, Sekai creates an opening for the Try Fighters, and they take advantage of this to escape the haunted castle and begin their counterattack. During the battle, Sekai senses that Toshiya is battling out of resentment toward the Gunpla Academy, and in order to overcome that grudge he musters all his strength to activate the Burning Burst and launch one last attack. The Try Fighters barely manage to win their second round, but all their machines have suffered heavy damage, and it appears that they won't be able to fully repair the Try Burning which was originally built by Sei Iori. But just then, Yuuma receives a message from his sister China.

After receiving spare parts for the Build Burning from his sister China, Yuuma is on his way back to the lodging house when he runs into a gang of delinquents. Yuuma risks himself to protect the parts, and is saved when Sekai and the others come running over. Meijin Kawaguchi spots someone hiding behind a tree watching the situation and tells him to come out. The person who appears is Junya Inose, a senior pupil who once studied the Jigen Haoh school of kenpo along with Sekai and Mirai. Sekai cannot hide his shock at this sudden and unexpected reunion, and wonders why the Junya who was once so kind would resort to such dishonorable tricks. Afterwards, Mirai tells him that Junya is listed as an alternate team member from Tenzan Academy, representing Miyagi Prefecture, their opponent in the upcoming quarterfinals. To determine Junya’s true intentions, Sekai must put his own feelings into his fist and challenge him in battle during the quarterfinals.

In the quarterfinals of the Gunpla Battle Japanese Championship, the showdown between Sekai Kamiki and Junya Inose, who are both students of the Jigen Haoh school of kenpo, has reached ferocious heights. To break the stalemate, Sekai activates the Burning Burst, but Junya activates his own Burning Burst as well. Even the original Gunpla technique that Sekai created is completely overcome. As he faces Junya, who is obsessed with the ultimate strength and seeks the extremes of strength to satisfy his own desires, Sekai continues to pursue his own kind of strength with a pure and earnest will. Putting their respective beliefs and feelings into their fists, the two combatants clash on. Sekai is hard-pressed by their difference in experience, and by Junya’s unfair attacks. But just as his consciousness fades due to the painful backlash of assimilation, Sekai is guided by a miraculous radiance.

The members of the best 4 teams in the Gunpla Battle Japanese Championship gather, and a drawing is held to determine the brackets for the semifinals. Match one will pit Shizuoka Prefecture’s independent Gunpla Academy, led by Wilfrid Kijima, against Tokushima’s Granada Academy, whose team includes the European junior champion Lucas Nemesis. In match two, Sekai Kamiki and his comrades from West Tokyo’s Seiho Academy Middle School will face Minato Sakai and Tendaiji Academy, representing Osaka. Before the first battle, sparks fly between the members of each team, centering on Sekai. Then, in a battle stage made up of floating islands, the curtain rises on the match between the Gunpla Academy and Granada Academy. Controlling the Crossbone Gundam X1 Full Cloth, Lucas begins a one-on-three battle against the Gunpla Academy.

At the end of the fierce first match of the Gunpla Battle Japanese Championship semifinals, the private Gunpla Academy has managed to achieve a narrow victory. The defeated Lucas Nemesis apologizes to Sekai because they won’t be able to fight in the final round, but says he’ll be waiting one step ahead, leaving Sekai with the encouraging prediction that they will meet again on the world stage. Meanwhile, Minato Sakai of Tendaiji Academy appears before Yuuma and Fumina to issue a declaration of war. Unable to understand Minato’s one-sided hostility toward Yuuma, Fumina asks the reason for it. This gives Minato an opportunity to spill out all of his previously accumulated feelings about Yuuma. Acknowledging Minato’s feelings, Yuuma apologizes from the bottom of his heart and proclaims his determination. With fresh resolve, the Try Fighters and the Build Busters commence the second match of the semifinals.

The teams advancing to the final round of the Gunpla Battle Japanese Under-19 Championship are the Try Fighters, who have narrowly defeated Minato Sakai’s team Build Busters, and Celestial Sphere from the private Gunpla Academy. In anticipation of the final match, which will be held two days later, both teams begin repairing the damage their machines suffered in the semifinals. Along the way, the Try Fighters hold a briefing at Mr. Ral’s suggestion. He has received detailed data, including records of the Gunpla Academy’s last battle, from Niigata’s Toritsu Academy, which the Try Fighters faced in the second round of the tournament. After seeing this, Yuuma begins to fret, even as he continues repairing his Gunpla. Simply restoring it, he feels, won’t close the gap between them and the Gunpla Academy. With this conviction, Yuuma gathers his resolve and decides to give all their machines a full remodel in the short time before the final round.

The final round of the Gunpla Battle Japanese Championship tournament has finally begun. Taking the initiative, the Try Fighters opt to fight inside a space colony. Sekai and Fumina split off from Yuuma, and both groups make preparations to intercept the Gunpla Academy. The audience members watch this quiet start with bated breath, until the silence is broken by Kijima’s Transient Gundam. Having anticipated the Try Fighters’ plan, Kijima launches a diversionary attack to distract them, and at the same time Yuuma finds himself in combat against Shia and Adou. As the teams continue trading blows in a fierce back-and-forth struggle, Yuuma and Fumina battle Shia and Adou of the Gunpla Academy to mutual destruction. Only Sekai and Kijima remain, fighting desperately to the brink of collapse, until they ultimately reach the time limit and usher in the first overtime battle of the tournament.

The final round of the Gunpla Battle Japanese Championship’s national tournament has ended in a victory for the Try Fighters. After the finals, Sekai suddenly leaves on a training trip. A few days later, the Gunpla builder’s contest known as the Meijin Cup begins. At the venue, Fumina meets up with Mr. Ral and with Yuuma, who has come for a Gunpla building showdown with Minato. Many of the rivals they previously fought in the regional qualifiers and the national tournament have also gathered here. The Meijin Cup awards ceremony begins, and Yuuma’s entry wins the Open Course category. As Fumina congratulates Yuuma on his prize, Sekai returns from his training trip. Meanwhile Minato, who refuses to accept the results of the judging, raises an objection to the Meijin. In response, the Meijin activates the Gunpla Battle system to that the two contestants can settle their dispute.