Haru Irei, along with his friend Kenta Sakazaki, visit the 1/1 RX-78-2 in Odaiba, Japan. In awe over its size, Kenta and Haru visit the merchandise store where there are many HGUC kits.While Kenta purchases an ecopla version of the MS-06F Zaku II, Haru tries to grab the last remaining 1/144 HG RX-78-2 Gundam Ver. G30th, but a girl grabs it instead and Haru runs right into the Gunpla stand. A box falls on Haru, and it is the GPB-X80 Beginning Gundam. Later, while watching 30th Gundam Perfect Mission, Haru decides to start building the Beginning Gundam. This causes Haru's father, Hinode, to reminisce about the times when he used to build Gunpla and how they had advanced since the late 70s. To help him out, Hinode lends Haru a pair of clippers and a modeler's knife to get rid of the excess gate plastic. While Haru is hard at work building, his friend Rina Noyama, an avid fan of Gunpla, stops by to visit. Haru eventually completes the Beginning Gundam and heads to the Axis Hobby Shop to participate in a Gunpla Battle.
When the trio arrives at the store, Kenta introduces Haru to the manager of the store. They then enter a Gunpla Battle room for 6 builders. After Haru suits up, another Gunpla Builder and ladies man Koji Matsumoto looks at the Beginning Gundam and is unimpressed by the suit. He then reveals his own RX-93-ν2 Hi-ν Gundam, given the color scheme of the original RX-93 ν Gundam. Koji then challenges Haru to a Gunpla Battle against his two female companions Igawa and Iwamoto. Since the Beginning Gundam wasn't in Koji's collection, he makes Haru a deal. If Haru wins the match, Koji would buy any Gunpla Haru wanted, but if Haru lost, he had to forfeit the Beginning Gundam. Though Haru hesitated, Rina stepped up and accepted the challenge for him. Haru suits up and launches in Beginning Gundam from White Base. With the playing field a simulation of Shizuoka City, Haru is teamed with two guys named Ono and Urushibata, who pilot a MS-09 Dom and a NRX-044 Asshimar respectively. While entering the battlefield, Iwamoto's blue MS-05L Zaku I Sniper Type starts taking shots at Haru, but he fires the beam rifle at the Zaku's leg stand and defeats it. Ono gets distracted by Haru and his Dom is defeated by Igawa in her pink AMX-107 Bawoo. While trying to take out the Bawoo, Haru is intercepted by Koji, who grapples the Gundam before deploying the Fin Funnels. Haru has a tough time against the Fin Funnels and loses the Beginning Gundam's left arm and crashes into the Bandai Hobby Center. Meanwhile, Urushibata's Asshimar is taken out by Koji's funnels. Suddenly Haru emerge from the ground and deploys 3 beam sabers to defeat the Bawoo. Koji and Haru battle again, and Haru manages to knock Koji into some netting, preventing him from deploying the funnels. As Koji struggles to break loose, the polycap holding the leg together snaps, to which Koji blames the manager for building it poorly. Haru said that the point was to build one's own Gunpla and stabs straight into the defenseless Gundam and wins the fight. As Haru calms down from his first battle, another man, Boris Schauer appears before a surprised Haru, piloting his customized GPB-X78-30 Forever Gundam. Stating that he's a Gunpla Meister, Boris challenges Haru to a one-on-one fight.