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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, and a moment later they mysteriously awaken on the shore, believing what happened was just a dream.
That night, two giant robots appear suddenly by the beach. A small creature calling itself 'Dung Beetle' appears and claims to be their guide. It then teleports the children into the black robot. They find Kokopelli already inside and controlling the black robot in order to defeat the white enemy robot. During battle he gives the children a brief tutorial on how to pilot the robot as he destroys the enemy. Once he has finished he tells the children that they are on their own now and sends them back to the beach. As the children are teleported out, one child observes Kokopelli whispering "I'm sorry".
Bokurano's stories tend to focus exclusively on one character - the next pilot. It starts with some background story on the character and their underlying motivations while building up to their battle. The chapters themselves are named after the character currently being focused on.
Takashi Waku is the first pilot of the robot, which is named "Zearth" by Maki Ano. Upon winning the fight, Waku is accidentally 'knocked' into the sea by Jun Ushiro. The second pilot, Masaru "Kodama" Kodaka, dies unceremoniously after defeating Cancer. Dung Beetle explains to the children that Zearth runs on life force, and the cost of every victory would be the life of its pilot.
The next two pilots, Daiichi Yamura and Mako "Nakama" Nakarai, lose their lives similarly. Nakama utilises Zearth's abilities to help save a classmate of hers and Daichi protects an amusement park so his siblings can go there. Before her victory death, she manages to give the others some pilot costumes that she sewed herself. Through Takami "Komo" Komoda, the military finds out about the children's connection with Zearth, and they are brought together for their own protection. The next pilot, Isao Kako, becomes too cowardly to fight. Chizuru "Chizu" Honda kills him, and becomes the next pilot. Before fighting the enemy robot, she seeks her revenge on the teacher who had abused her sexually. While attempting to kill him, she is stopped by her sister. Both her life and her baby's life are taken as Zearth's payment, revealing that there is another person besides Kana Ushiro who is exempt from the contract.
Kunihiko Moji is the next pilot. Their enemy, Gonta, traps them, but Moji uses the spinal cord of Zearth to attack Gonta's core. It is revealed that Zearth's cockpit resembles that of their enemies. Maki, the next pilot, realizes that they are in an alternate universe when an unknown fighter jet attacks them. She pries open the enemy's core and reveals the human pilots inside. Dung Beetle explains that these battles are to weed out parallel universes.
Great anime you should all look at it. Its sad though