In the upgraded GBN, Hiroto continues to play as a solo mercenary. He is greeted by a Diver named Kazami, who suggests that they team up. Hiroto flatly rejects the idea, but Kazami appears undeterred. His goal is to attempt a rumored hidden mission.

Thanks to Freddie's enthusiasm for the legendary force, Hiroto and his teammates have had no choice but to call themselves "Build Divers." All the members have different reactions, but Hiroto has a particularly strong feeling about the name. Meanwhile, the four of them play Freddie's mission once again, and Freddie invites them to visit his village.

The Build Divers have accepted a mission to protect Freddie's village. In their rehearsal battle, however, they realized that their poor teamwork will inevitably result in collateral damage. Hiroto proposes a secret plan that will enable them to clear the mission without harming the village.

Believing that Freddie's mission is an ongoing story mission newly added to GBN, the four decide to continue the adventure. Freddie introduces them to members of the Resistance, who tell the Build Divers about their planned counterattack operation. The next task is a diversionary mission to support an attack on the One-eyes' giant base in the desert.

On the day of the operation, Parviz is late to arrive. Lamenting his previous incompetence, he tells the other Build Divers that he wants to quit. Kazami desperately tries to stop him, May is calm, and Hiroto is excessively realistic. Parviz remains determined, but then he is forced to begin the mission against his will.

While Parviz experienced great growth in the previous mission, Kazami alone is resentful at his own inability to distinguish himself. Meanwhile, the Build Divers head for the Resistance base where Freddie's brother Jed is stationed.

Though Gojo has asked him to look after Kazami, Hiroto is unable to figure out Gojo's real motive. And Kazami, unable to find a way to lessen the huge gap between his own ideals and his current state, can only agonize in vain. With their teamwork in this hazardous state, an escort and evacuation begin.

Hiroto and Kazami have made a small but very important improvement in their relationship. However, the Build Divers and the Resistance are now overwhelmed by the attack of the mysterious Gunpla known as "Seltsam." The pendant that Muran entrusted to Hiroto and the others seems to become a key to turn the tide, but… Meanwhile, May begins gathering intelligence at Magee's bar.

Parviz and Kazami have finally begin to realize that the Build Divers are a team. But Hiroto suggests that he clear the next mission with his own strength alone. May questions him doggedly, but Hiroto is merely bewildered by this.

May's Wodom Pod has been destroyed while shielding Hiroto from an attack, and from it emerges May's mobile doll form. May is an EL-Diver, an electronic lifeform born from GBN itself. As the other Build Divers react with amazement, Mobile Doll May takes the offensive against the Gundam Seltsam.

The Space Crossing festival is over, and the Build Divers and the Resistance prepare for their next mission. Hiroto and the others have figured out how to open a door located in the lobby of the surface station connected to the orbital elevator, their next objective. They decide to log out for the moment to make further preparations before continuing ahead. The stage for what appears to be their last mission will be outer space.

After a mutually frustrating conversation with the entity that calls itself Alus, the Build Divers temporarily withdraw from the moon. Awaiting them are a tremendous number of One-eyes, which appear to be led by the Gundam Seltsam. Then Hiroto and the others are shocked by another new development.

After a fierce but futile battle, the satellite cannon hidden inside the moon has unleashed a devastating beam. Its effects reach beyond the planet Eldora, extending to all of GBN and even the real world where Hiroto and the others live. It appears that their previous battles may not have been all a game, but actual events instead. Hiroto is completely bewildered by this unimaginable development. But he is no longer alone. It is now inevitable that the Build Divers must meet in real life.