Seeking adventure during a school field trip, fifteen kids stumble upon a strange man in a cave, who invites them to play a game. But it turns out, the game is all too real.

A strange creature named Koyemshi introduces itself to the group. Takashi is chosen as the next pilot of Zearth, and he resolves to be a "hidden hero" and protect the Earth.

Questions remain in the wake of Takashi's death, the most pressing of which being, how did Takashi die? Both the kids, and the police, want to know. Amidst the grief and uncertainty, the next pilot is chosen.

Masaru's family life has made him come to divide the world into two types of people: those born to die, and those born to survive. When it's his turn to fight to protect Earth, which type will he end up as?

The children realize just what it means to be chosen as a pilot for Zearth. Meanwhile, the adults finally make their move, as the military gets involved, both with Koyemshi, and Zearth itself.

The next pilot is Kako, but the other kids can't find him, though Chizu has an idea of where he might be. When the next enemy appears, the military makes an attempt a first strike.