Gate Keepers (ゲートキーパーズ, Gēto Kīpāzu) is a role-playing video game for the PlayStation. The game was then adapted into a manga series written by Hiroshi Yamaguchi and illustrated by Keiji Gotoh and an anime series produced by Gonzo, and first aired on April 3, 2000.
A six-episode original video animation sequel, Gate Keepers 21, was released in 2002.
The story is set in 1969, a period of time in which Japan is experiencing intense economic and social development after the end of World War II in 1945. Unbeknownst to humans, alien/interdimensional beings have emerged with plans to take over the world by sending numerous agents to wreak havoc in cities, turning people into robotic minions. They are referred to as "Invaders" (インベーダー Invēdā).
In an attempt to confront the Invaders and defend the planet, an elite but highly secret organization of peace-keepers called the Alien Exterminating Global Intercept System (more commonly known as A.E.G.I.S.), was set up with special funding from the government. They rely on the ability of "Gate Keepers", who have the power to open dimensional "gates" of a paranormal energy that give them their superpowers. These superpowers are the only weapons that have any effect on Invaders.
Although A.E.G.I.S. has branches around the world, the series focuses on the Far East division in Japan. The headquarters of the Far East branch of A.E.G.I.S. lies beneath Tategami High School, a facade created by the organization to mask the active recruitment of new Gate Keepers. Since many of the candidates were High School students, the location allowed the agents to be enrolled in school and be available for a mission at a moment's notice.