
During a summer camp, 15 children, 8 males and 7 females, find a grotto by the sea. Deep within they discover working computers and some electronic equipment, and later the owner, a man called Kokopelli. Kokopelli claimed to be a programmer working on a brand new game, in which a large robot has to defend the Earth against fifteen alien invasions. He persuades the children to test the game and sign a contract. All but one of them signs; barely a moment later they mysteriously awaken on the shore believing what happened was just a dream.

Fifteen children at a summer school program encounter the mysterious Kokopelli and agree to be testers for a game he claims to have completed recently. Soon, they are summoned into the cockpit of a giant mecha, with Kokopelli piloting. Thus the first round takes place.

The children start having second thoughts about the game, but a floating being known as Dung Beetle appears and teleports them to the cockpit of the mecha, which the group later dubs Zearth. On the evening of the same day, a new enemy appears, and Takeshi Waku is chosen to fight it.

Takami "Komo" Komoda reveals the truth to her father, and while Waku's funeral is being held, Masaru "Kodama" Kodaka is selected to be the third pilot.

Kodama fights the third enemy without caring about his surroundings, causing many casualties in the process, until he discovers the meaning of losing someone important to him.

After the children discover the fate that awaits them, they are assembled and interrogated by the military, except for Isao Kako, who coincidentally is the next chosen pilot.

The children try to find Kako without success, until Chizuru "Chizu" Honda discovers where he is hiding and tries to cheer him up. However, Kako has other plans for her.

The story of Chizu's relationship with her teacher is revealed, before she is selected to replace the deceased Kako.

The fourth battle begins, but Chizu is more worried about taking revenge on her teacher than facing her enemy.

Selected to fight the fifth enemy, Daiichi "Daichi" Yamura's final wish is to spend his remaining time happily with his siblings, but his plans are ruined when the battle starts sooner than he expected.

Bullied by her classmates because of her mother's questionable occupation, Mako "Nakama" Nakarai, after being chosen to engage into the sixth round, resorts to extremes to arrange money enough to complete a personal project of hers in time.
Available on: TV Aichi, Tokyo MX, tvk, Sun TV