Freddie, an inhabitant of the planet Eldora, sets foot inside a ruined temple, carrying with him a book he accidentally discovered in a storage room. His curiosity leads to an encounter with Hiroto and the other Build Divers, and nobody could imagine what will result from this beginning...

Once again, Hiroto and the Build Divers make contact with Freddie and stand on Eldora's soil. Their sense that the planet Eldora really exists, and isn't just a GBN Story mission, is reinforced. But meanwhile, where their Gunpla are concerned, they must deal with a situation dramatically different from before.

Riding in a balloon made by collecting the lanterns from the Space Crossing festival, Parviz and Freddie go to meet the sacred beast Cuadorn, which dwells in the floating temple known as Milaag Mountain. Buffeted by strong winds, the balloon continues its ascent, but ahead of it lies a huge thundercloud like nothing they've never seen before.

Hiroto and the Build Divers have finally met with the sacred beast Cuadorn, only to be rejected. But after they unflinchingly convey their feelings towards Eldora, Cuadorn opens its silent mouth. As it begins to speak, it tells them of the lightning from the moon that struck Eldora, and of Alus, the one who unleashed it.

Hiroto and the Build Divers have succeeded in turning Milaag Mountain, the home of the sacred beast Cuadorn, into their new base. As they hold a strategy meeting to save the people of Eldora from the One-Eyes, images of Hiroto's own Gunpla and the Alus Earthree Gundam created by Alus are superimposed in Hiroto's complicated thoughts.

Their battle with the Alus Earthree Gundam has ended in victory for Hiroto and the Build Divers. In front of its wreckage are the Earthree Gundam and the Beam Shoot Rifle U7, which has been thrust into the ground. As Hiroto stares at the rifle which looms like a gravestone, a buried memory is revived within the depths of his heart.

Once again, Hiroto and the Build Divers gather in real life. To save the people of Eldora from the One-Eyes, they must power up their Gunpla to resist the powerful new enemies created by Alus, and discuss how to rescue Masaki Shido, whose mind is still trapped on the planet Eldora. Then Parviz makes a surprising proposal.

Muran has entrusted Hiroto, Kazami, and May with the task of rescuing Masaki Shido, and they begin searching for the Seltsam. However, their radar instead detects a huge force of dozens of enemy machines. Meanwhile, in the ruins of Milaag, Parviz and Freddie continue working to repair Cuadorn's injured wings.

Thanks to the efforts of Hiroto and the Build Divers, Masaki Shido has been successfully rescued. Hiroto, Kazami, Parviz, and May gather at The Gundam Base to pay a visit to the awakened Masaki. Suddenly, they hear the roar of a motorcycle engine. The rider is someone they never expected.

In preparation for the final battle with Alus, Magee has arranged a rehearsal mission based on the Lotus Challenge, one of the hardest in all of GBN. Hiroto and the Build Divers are the challengers, and awaiting them are a horde of famous and powerful Divers, including the Force members of the original Build Divers.

Alus has chosen to forcibly invade GBN in order to eliminate the people of the Gunpla. But lying in wait for his forces are the Divers of the Coalition of Volunteers, assembled now for the third time. The mission of Hiroto and the Build Divers, which began on the planet Eldora, finally enters its last stage.