15 kids find a mysterious man living in a cave with high-tech equipment. He claims to be a game developer and lets them test his creation, but once they start playing, they can't find a way to stop or exit.
GameFifteen 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.
Zearth
D2
ZearthThe 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.
Secret
D3
SecretTakami "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.
Strength
D4
StrengthKodama respects his father for doing anything to get what he want. He believes he and his father are worthy of being chosen. Then, the system chooses him as 2nd fighter, and teleports the children into Zearth.
Weakness
D5
WeaknessAfter 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.
Lust
D6
LustThe 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.
Wound
D7
WoundThe story of Chizu's relationship with her teacher is revealed, before she is selected to replace the deceased Kako.
Revision
D8
RevisionThe fourth battle begins, but Chizu is more worried about taking revenge on her teacher than facing her enemy.
Family
D9
FamilySelected 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.
Companion
D10
CompanionBullied 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.
Life
D11
LifeNagi, a childhood friend of Kunihiko Moji's needs a heart transplant, but so far the only compatible donor found is Moji himself. While dealing with Nagi's drama, he is selected to fight the seventh enemy.
Blood Relative
D12
Blood RelativeMaki Ano is in awe as her foster mother is about to have a baby. She hopes to at least witness her little brother's birth, but when she is appointed the pilot for the eighth round, she is left with little hope to be able to do so.
Earth
D13
EarthDuring Maki's fight, the children discover the true nature of the enemies they are battling, and what really is at stake on every single bout.
Perplexity
D14
PerplexityYosuke Kirie wonders if he will find the resolve to fight in the next battle. While Mitsumi starts to look for means to protect the remaining children, Masamitsu discovers her secret.
Self-Destruction
D15
Self-DestructionThe ninth round begins, but after witnessing his mother's miserable life, Kirie refuses to fight. Just when his companions are about to lose hope, something that nobody expected happens.
True Identity
D16
True IdentityTamotsu helped Kirie's mother to find a job. Kirie relieved that she got cheerfulness again. Meanwhile, a Diet member Komoda raised a question in a Diet about Zearth according to the report that Tanaka gave him secretly.
Affection
D17
AffectionChosen to the tenth round, Aiko Tokosumi's life is turned upside down when a scandal involving her father brings up turmoil to her household. But she ends up finding in Kanji the strength to carry on with her duty.
Reality
D18
RealityKomoda plans to talk about the Earth crisis when he announces that he'll resign his position at a press conference, however, someone tries to kill him. Officer Seki and Tamotsu support Komoda's wife and daughter to escape.
Mother
D19
MotherTamotsu reveals to Jun Ushiro who his real parents were and tells him their story.
Ego
D20
EgoMachi reveals to the remaining pilots all she knows about the battles, and how she and her brother got themselves involved on them.
Truth
D21
TruthWhile Kanji fights the Twelfth enemy, the real objective of the masterminds is revealed. Later, Jun receives a proposal from Dung Beetle that may save his life if he accepts.
Distance
D22
DistanceJun takes Kana to her father's house, having Machi traveling with them. On the way, he reminisces about his infancy days, and later, he asks Machi's help to protect Kana from Dung Beetle's intentions.
Snowscape
D23
SnowscapeThe human armies decide to intervene during the thirteenth battle, while Machi betrays Dung Beetle and becomes the next pilot in Kana's place.
Story
D24
StoryJun declines Seki's offer and becomes the pilot for the final round. During the long battle, he reminisces about his fallen comrades while struggling to save the Earth once and for all.
