西暦2001年。 長い不景気が続き、凶悪犯罪の増加、環境破壊、道徳観の崩壊、国際情勢も安定せず、明るい未来なんて期待できない毎日。 インベーダーが行動を再会するにはうってつけの時代。 人類は今まさにインベーダーに支配されようとしていた。 そんな中、民間人で結成された地下反抗組織イージス・ネットワークに所属し、 インベーダーを倒すことで報奨金を得ているインベーダー・ハンター達がいた。 彼らは疑似ゲート能力を使いこなし、インベーダーを狩っている。 その一人、五十鈴綾音は偶然にもある力をつかう真鶴美羽を目撃してしまう。 本物のゲート能力者を見つけた綾音はそれをイージス・ネットワークに報告する。 ある日、「自分の力が何か知りたくない？」と綾音に誘われた美羽は、彼女についてゆく。 そこへ突然、人の姿をした大量のインベーダーが現れる！
ゲートキーパーズ21 (シーズン 1)
Encounter 0.0
放送日: 2002-04-24
上映時間: 25 min
概要: Ayane Isuzu destroys some Invaders, and collects the crystals they leave behind. While looking for more Invaders, she sees a girl fly across the sky. After school the next day, Ayane meets with a mysterious man who tells her to locate a girl called Miu Manazuru, for she is a Gate Keeper. Ayane gives the man a bag of crystals in exchange for money. That night, Ayane approaches Miu, and tells Miu to join her in her effort to destroy the Invaders. Miu is wondering what to do, when they are suddenly surrounded by Invaders...
Mad Dash 0.0
放送日: 2002-07-17
上映時間: 25 min
概要: Ayane and Miu are chasing after a truck under control of the Invaders. Ayane manages to throw off the police that were following, and then tells Miu to fly over to the truck. Miu almost succeeds, but hits a highway sign instead. The next day, Miu and Ayane are at their school, when they see what appears to be a ghost. They decide to follow it, and in the process stumble upon an elevator that takes them to an underground complex. Down there they discover something that can help them find the Invaders.
Late Summer 0.0
放送日: 2002-08-21
上映時間: 25 min
概要: Miu's school friends notice that Miu seems distant depressed. Miu's friends decide to take her to a karaoke lounge to try to cheer her up. They are in a singing room when an interruption occurs in the form of a power outage. Suddenly, Invaders start swarming all over the place. Ayane hears about the Invaders at the karaoke lounge, and goes to help.
Ayane 0.0
放送日: 2002-09-19
上映時間: 25 min
概要: A new Gate Keeper, Satoka Tachikawa, has appeared. She destroys Invaders to collect their crystal remnants for money. Ayane and Miu are outside of school when Satoka confronts them. She attempts to get Ayane to answer a question about her past, but Ayane manages to slip away. Later, Reiji notices signs of Invader activity, and Satoka rushes off to fight them.
Miu 0.0
放送日: 2002-10-17
上映時間: 25 min
概要: Miu's decides to visit Reiji at his headquarters, where they talk more about the Invaders, and Ayame.
The Sound of Wings 0.0
放送日: 2003-01-08
上映時間: 31 min
概要: The Gatekeepers face their final confrontation against the Invaders.
シーズン
エピソード 6