Irregular Hunter X: The Day of Sigma
English title: Megaman X - The Day of Sigma
Japanese title: イレギュラーハンターＸ
Alternative titles: Irregular Hunter X, MegaMan Maverick Hunter X: The Day of Sigma
Type: OVA
Source: Game
Episodes: 1
Status: Finished Airing
Aired: Dec 15, 2005
Duration: 30 min
Rating: G - All Ages
Studios: Xebec
Licensors: Capcom
Genres: Action, Sci-Fi

The year is 21XX. Reploids are commonplace now, after Dr. Cain rediscovered Dr. Light's old lab and based several designs off of Dr.Light's original, called "Megaman X." X, meanwhile, has joined the Maverick Hunters, and works with unit leader Zero under the command of General Sigma. It is their job to terminate rogue reploids, those who have become violent. 

(Source: ANN)