Gate Keepers

 is a role-playing video game developed by Entertainment Software Publishing and published by Kadokawa Shoten for the PlayStation. The game was then adapted into a manga series written by Hiroshi Yamaguchi and drawn by Keiji Gotoh and an anime series produced by Gonzo, and first aired on April 3, 2000. A six episode original video animation (OVA) sequel, "Gate Keepers 21", was released in 2002. The main characters in the OVA sequel were the next generation of Gate Keepers.
All "Gate Keepers" series follow the same basic premise and share most of their characters, with some major discrepancies (mainly involving the character Reiji Kageyama). A character from the game, Francine Allumage is completely absent from the anime. Another character from the game Misao Sakamori, was replaced in the anime with the new original character Megumi Kurogane (though Misao does make a guest appearance towards the end of the anime).
Plot.
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 .
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.
Characters.
A.E.G.I.S. members.
"Names with asterisks indicates an anime-only character."
Media.
Manga.
A three-volume manga series, created by Keiji Goto and following the plot of the video game, was published by Kadokawa Shoten. Two volumes were released in the United States by Tokyopop.
Anime.
The anime series was produced by GONZO, written by Hiroshi Yamaguchi, and was directed by Koichi Chigira. The network WOWOW aired the 24 episode series from April 3 to September 8, 2000. In 2001, Geneon Entertainment USA (then known as Pioneer) acquired the series and released them in eight volumes on DVD and VHS. In 2004, Geneon re-released the series under the Signature Series label. In 2007, Geneon USA was soon dissolved and left the series (including the GK21 OVA's) out-of print.
Light Novel.
"Gate Keepers 1985" (-C0193) tells the story of the 15 years leading up to "Gate Keepers 21".