Gunpla Battle referees led by Takeshi Iori conduct a raid on a Gunpla Mafia hideout in London and find that it has been abandoned. Gunpla master Chinan calls Takeshi and reports that both he and Ral also struck out in tracking down the criminals. In Japan, Ricardo Fellini has a drink at the memorial park erected at the former site of the 7th Gunpla Battle Championship. Fellini thinks about everyone who fought during the tournament and greets Meijin Kawaguchi the 3rd (aka Tatsuya Yuuki), who is also visiting the memorial. Nils Nielsen shows up and takes them to the new Yajima Stadium, where he offers to give them a special tour before the dedication ceremony. Yuuki and Fellini are surprised by the new large-scale battle system, as well as seeing Sei Iori, China Kousaka and Mao Yasaka, whom Nils also invited. Fellini jokes about the three of them not growing up yet. Mao declares that he intends to win tomorrow’s exhibition battle, and Fellini boasts about his upgraded unit. Although Nils has retired from battle, he plans to participate in the battle tomorrow. Yuuki asks Sei what Gunpla he’s going to use, and Sei reaches for his Build Strike Gundam Cosmos, but can’t find it. China recalls that en route to the stadium, a man in a trench coat bumped into Sei while he was gawking at a Gunpla display in a window. The lights in the stadium suddenly go out, followed by every exit closing. The Gunpla Mafia appear, and their leader declares that he wants to challenge them to a real-time Gunpla Battle for supremacy over the Gunpla world. Sei thinks they must be joking, but Yuuki wants to fight them and weaken the Gunpla Mafia. Nils agrees, followed by Fellini and Mao. Sei decides to fight and use his new incomplete Gunpla, the Star Burning Gundam. The battle begins in a large custom level created by the Gunpla Mafia. Sei’s Star Burning launches, followed by Mao’s Gundam X Jumaoh, Fellini’s Gundam Fenice Liberta, Nils’ Ninpulse Gundam and Yuuki’s Amazing Z’Gok. Yuuki warns everyone to expect traps since the level was created by the Gunpla Mafia, and Nils adds that they won’t fight fair. Fellini blasts a hole in the colony tower, which leads them to the surface of the Moon. Nils tells everyone to go ahead, and he suddenly launches an attack to reveal a cloaked GM/GM. After destroying the first unit, he then comes over a dozen more GM variants. The rest of the group fly through a tunnel and emerge in a large forest filled with roses. Fellini stays behind to fight a gold Baund Doc piloted by Gawain Oakley, a former member of Team Nemesis. Fellini taunts Gawain about working for the Gunpla Mafia, and he angrily responds that he needs money to build the most beautiful Gunpla. Fellini fires his buster rifle, which Gawain is able to deflect thanks to its diamond coating. Kirara watches the battle and urges Fellini to fight on. Fellini gets in close on the bottom takes Gawain out in his weak spot. He then loses control of his machine and is shocked by the Gunpla that shows up.
In the Moon area, Nils destroys more and more GMs and uses a wide-range attack to destroy multiple units. A GM/GM closes in to attack and is destroyed by China’s Beargguy III. Machine gun turrets open fire on Yuuki, Sei and Mao, but they easily dodge. The path ahead splits into three paths, so everyone splits off on their own. Mao emerges in a city and is attacked by Musha Gundam Mk-III pilot Nenene, who uses her large breasts to distract Mao and attack him. Yuuki reaches the Jaburo underground and is blocked by J’s GM Z’Gok. J suggests fighting in the nearby lake since they both have amphibious units, but Yuuki refuses because he knows the lake is filled with paint thinner that melts plastic. Yuuki attacks and easily destroys J’s unit. Mao, distracted by Nenene’s breasts, is unable to fight back and thinks about how disappointed Misaki will be in him. Mao declares that Misaki is the only one for him and fires his four satellite cannons, which destroys Nenene’s unit. Sei enters a desert and is shocked to find the Gunpla Mafia leader using the Build Strike Cosmos. Sei opens fire on his opponent, who is able to dodge easily. Fighting against his own unit, Sei sees the flaws in its construction. Sei grapples the unit from behind and asks the leader to stop, but he refuses. Sei then comes under attack from the massive Psycho GM, which is able to destroy his shield. The Psycho GM grabs the Star Burning, but its arms are then cut off by Yuuki. Mao arrives and provides cover fire, but the Gunpla Mafia leader shuts down all their units. China arrives carrying the Fenice Liberta so it can fire its rifle. Fellini and Nils explain that the Gunpla Mafia is manipulating the Plavsky particle levels, which allows them to stop unit movement. The Psycho GM conducts a scattering beam attack, and the leader boasts about the Gunpla Mafia’s power. Sei stands up and vows that no one will acknowledge the Gunpla Mafia and their cheap tricks. The Star Burning Gundam suddenly moves when Reiji appears out of nowhere to help Sei. Since there aren’t any Plavsky particles to move the Gunpla, Reiji creates some with the jewel in his bracelet. Sei gives instructions to Reiji and explains that he built this Gunpla for him. Reiji activates the RG System and uses a Hyper Star Burning Knuckle. The punch destroys the Psycho GM, thus ending the battle. The Gunpla Mafia members find that the leader, Mikio Mashita, has abandoned them and is attempting to escape. However, he’s arrested at the door by Takeshi and his men. The rest of the members are rounded up, and Takeshi thanks everyone for their help. Sei asks Reiji how he came to Earth, and he explains that he borrowed the Arista that Sei gave to Aila. Everyone wants to hang out with Reiji, but he answers that he has to do something else: have his long-planned fight with Reiji. The two use the Star Burning and Build Strike Cosmos to fight in a forest of sakura blossoms. The two activate their RG Systems and charge at each other. As the battle moves to space, Reiji comments that Sei has grown into a strong fighter. One year later, Sei hides a secret inside a trophy at Seiho Academy’s Gunpla club room.
Coming more than three years after the end of Build Fighters, this ONA serves as both an epilogue to the original series and as a bridge to Try. The lack of most of the original cast in Try was noticeable, so it’s nice to see them all show up again here. We see more of Sei as a fighter beyond the brief glimpse at the end of the original series, along with the missing pieces of the puzzle that led to the Build Burning Gundam’s creation. The Gunpla Mafia strikes again, and we learn that their leader is Mikio Mashita, the twin brother of the former PPSE chairman who was the main villain of the TV series. As usual, references are tossed out to past shows, and the ridiculous fan service with Nenene and her outfit is a callback to Gundam X‘s Ennil El. Reiji makes a surprise appearance at the end to help Sei smack down another Mashita, and we finally get to see some of the fight they vowed to have. Although the Battlogue shorts have featured cast members from both shows, at this point it’s not clear if we’ll ever see all of the original cast again. If this is the end of their story, it’s a pretty fitting conclusion.