Gate Keepers 21 is a oVA anime that premiered in spring 2002.

About the production: the story comes from a video game, there are 6 episodes of about 30 minutes and its current status is "finished".

Its main genres are action, drama and sci-fi.

On AniList, Gate Keepers 21 has an average score of 63%, an average score, and appears on 2,294 users' lists.

The franchise continues in or follows from: Gate Keepers.

32 years have passed since the initial defeat of the Invaders. A.E.G.I.S is all but dismantled now and has become an underground organiziation consisting of only a few Gate Keepers left to save humanity. One of the members, Ayane Isuzu, is sick of society as a whole, though she continues to defeat the Invaders out of spite for her father. Suddenly, she learns of the revival of Machine General (Kikai Shogun) and Devil Count (Akuma Hakushaku), but a mysterious ghost girl now accompanies them. It is up to Ayane and the remnants of A.E.G.I.S to stop them and save humanity once again. (Source: Anime News Network)

Official synopsis from AniList.