The sixth main entry in the Mega Man X series, it was first released on the PlayStation in Japan on November 29, 2001, and was later made available in both North America and Europe.

The plot of Mega Man X6 takes place during the 22nd century, where humans live alongside fully sentient robots called "Reploids".

The game follows shortly after the events of Mega Man X5, in which the Reploid Zero sacrifices himself to help save planet Earth from a global catastrophe caused by series antagonist Sigma.

As the world recovers, an entity known as the "Zero Nightmare" has begun spreading chaos, prompting series protagonist X to investigate.

Zero can be unlocked as an additional playable character by completing hidden, optional stages, retaining his sword-based gameplay from previous games.

Critically, Mega Man X6 has received mixed reviews for its recycled narrative and high difficulty derived from poor level design and is frequently regarded by fans as among the worst games in the franchise.

Players initially play as series protagonist X, who is skilled at shooting with his X Buster and can now wield the Z Saber in close-quarters combat.

[2][3] Zero can be unlocked after finding and defeating the boss Zero Nightmare, and he plays with a unique set of abilities, including a more refined Z-Saber fighting style and a double jump.

As a result of the space colony's impact, Earth's surface has been rendered largely uninhabitable, forcing the human population to take refuge underground.

A week later, Gate loses his sanity as he secretly experiments on the mysterious item and declares his intention to turn Earth into a utopia for high-class Reploids.

[18] If Zero defeats Sigma, an unknown scientist seals Zero away for research for the next 102 years, as Zero is worried about the potential of his DNA and believes X can protect the peace in his absence.

The designs for other characters also feature unique traits, including Gate as a "merging of scientists and combatants, High Max as "big and strong", and the DNA-like Nightmare.

The game also features the opening vocal songs "Moon Light" and "The Answer" by Showtaro Morikubo and the ending theme "I.D.E.A."

[29][30] According to the Japanese magazine Famitsu, Mega Man X6 was the seventh best-selling game in Japan during its week of release, with 39,318 units sold.

[39] Dengeki Online reported that Mega Man X6 sold a total of 106,980 units in Japan by the end of 2001, marking it as the 109th best-selling game of the year in the region.

[43][35] Giancarlo Varanini of GameSpot was disappointed by the execution of the Nightmare System and item collection, which added variety and longevity but were not important to completing the game.

[36] Gaming Age praised the production values for producing aesthetically pleasing stages and cutscenes retaining good audio.

[36] In retrospect, 1UP.com referred to Mega Man X6 as "sloppy", citing multiple issues within its design, such as repetitive stages and background images.

[44] Despite panning the narrative for recycling events from the franchise, Zoey Handley of Destructoid felt that the gameplay was the same as the older games though she also highlighted the poorly implemented Reploid Rescue system, which effectively forced the player to save them all in order to progress through most of the most challenging stages.