Neo Arcadia

Neo Arcadia (ネオ・アルカディア) is both the metropolis and government that much of the activities in the Mega Man Zero series takes place in. The latter is the main antagonistic force throughout the Zero series. Neo Arcadia was created by X a century before the first Mega Man Zero game, and is ruled by him along with the Four Guardians and the Eight Gentle Judges. Neo Arcadia was considered a utopia, but after X disappears to seal the Dark Elf, a copy of him was created by Ciel to take his place without the knowledge of the population. When Neo Arcadia falls in an energy crisis, Copy X decides to dispose of several Reploids by judging them as Mavericks for the good of mankind in order to avoid large energy consumption. Innocent Reploids are labeled as Mavericks, and Ciel, the scientist who created Copy X, formed a Resistance to fight against him. He is defeated by Zero in the first game. His death is not revealed to the public, and Sage Harpuia secretly rules Neo Arcadia during Mega Man Zero 2.

Dr. Weil revived Copy X in Mega Man Zero 3 and brainwashed the Eight Gentle Judges. Copy X returns to his post, and makes Weil second in command, demoting the Four Guardians. Copy X died during a fight against Zero, when a trap set by Weil in his body exploded. Weil had his death planned from the beginning to take his place as ruler of Neo Arcadia, by using "Ordinance #8". His tyranny affects not only Reploids, but also humans, as any who opposes him is considered a Maverick and will be disposed of. In Mega Man Zero 4, a caravan escapes from Neo Arcadia to Area Zero, in hopes to live peacefully, but Weil decides to use a space cannon, Ragnarok, to destroy everything outside Neo Arcadia, leaving no place to hide and escape from him. Craft attempts to kill Weil by using the Ragnarok against him in Neo Arcadia. Zero was able to defeat Craft, but not before Craft fired Ragnorok and destroyed most of Neo Arcadia, claiming over 20,000,000 victims. Weil survived the Ragnarok's laser and went to Ragnarok after Craft's death. When he was ready to destroy Area Zero, Zero fought against him in the Ragnarok. Weil supposedly died in Ragnarok's destruction (he returns as Biometal W in Mega Man ZX), whilst Zero was MIA. Neo Arcadia had no ruler after this, and the population started to move to Area Zero.

In the Rockman Zero manga, Neo Arcadia is ruled by Cial (Ciel's older sister) and the Four Guardians, which were created by her. This version of Neo Arcadia is more strict than the games, which is visible in the first story when Fefnir hurts an old human to locate a Reploid.

In Marvel vs. Capcom 3: Fate of Two Worlds, Neo Arcadia appears in Zero's ending, the character in question misplaced in the series timeline by a wayward Silver Surfer, commenting on there being another Zero but looking different than the X series version and going by the Mega Man prefix instead.

Area X
Area X (エリアX), also known as the Neo Arcadia Core and Neo Arcadia Headquarters (ネオ・アルカディアの本部), is a control room from the first game located on a stationary satellite at an altitude of 36000km. The area governs all of Neo Arcadia's unmanned space stations.

Area X-2
Area X-2 is the central command center of Neo Arcadia in Mega Man Zero 3, ruled by Copy X and Weil. From Area X-2, they command the entire Neo Arcadian army.

Neo Arcadia Shrine
The Neo Arcadia Shrine (ネオ・アルカディアの神殿), also known as the Holy Region (聖域), is the path that leads to the Neo Arcadia Tower at the center of Neo Arcadia. It is surrounded by a completely artificial, sterile environment, and is heavily guarded by a building designed like an ancient shrine that houses an elite force of Mutos Reploids. Zero faces two Pantheon Aces, Asura Basura, and Herculious Anchortus in his way to the tower.

Neo Arcadia Tower
The Neo Arcadia Tower (ネオ・アルカディアの塔) is a tower the first game located between the Neo Arcadia Shrine and Area X. Zero fights against the Rainbow Devil in the top of the tower. The tower used to be an orbital elevator for transportation between the Earth's surface and the moon, which was destroyed in the Maverick Wars. It was repaired and now is used to foil would-be infiltrators of Neo Arcadia.

Train of Neo Arcadia
The Train of Neo Arcadia (ネオ・アルカディアのれっしゃ) is a Neo Arcadian train that was transporting goods in Mega Man Zero 2. Elpizo asks Zero to seize the train's supplies for the Resistance, and he fights against Panter Flauclaws between two trains.

Sub Arcadia
Sub Arcadia, known as Under Arcadia (アンダー・アルカディア) in Japan, is the underground power source of Neo Arcadia, it acts as a central core for all of Neo Arcadia's machinery. Omega was sending Dark Elf's powers out to the world from this location. During the fight between Zero and Omega, they fell deep underground into the Underground Laboratory.

Yggdrasil
Yggdrasil (ユグドラシル) is the sanctum where the original X sealed the Dark Elf. Zero fights against Elpizo in this locale in the end of Mega Man Zero 2.

It seems to be located at the very core of Neo Arcadia. It also houses 6 transport ports to other places (most likely another sections of the building), where Zero fights 7 different bosses. X´s original body rests at the very top, using a huge power generator to hold the seal of the Dark Elf. It is named after the world tree in Norse Mythology.