Lyoko (pronounced either l'yoh-koh or lee-oh-koh) is a virtual world, contained and accessible by a Supercomputer within the Factory. It was designed by Franz Hopper, as a means of digitally representing and accessing the abilities of the Supercomputer.
The world is divided into five separate Sectors, all with their own unique features. Each sector is isolated from the others by a physical representation of the Internet known as the Digital Sea. A sparse, barely-populated world, the most notable landmarks on Lyoko are the 86 Towers scattered around it; 21 in each main sector and 2 in Sector Five. These towers act as data processing nodes, pathways to the real world, and safe havens for those on Lyoko.
In French, it is spelled as Lyokô. In Japanese, it is known as Ryoko, due to the Japanese language having a lack of an equivalent to the letter L.
It is never revealed in the show where the world's name came from. In the Code Lyoko Chronicles, however, it is revealed that Aelita came up with the name as a child.
According to Franz Hopper's diary, Lyoko and X.A.N.A. were originally meant to destroy Project Carthage, which was a military project designed to disrupt enemy communications. It began sometime in 1974. Franz Hopper left the project roughly 2 decades later. From the information given, it is not clear if the project was ever shut down. Sector Five may be the 3-dimensional representation of that project, as indicated by its password window "welcome to Carthage". Why Hopper wished to destroy it is unclear, but he built the quantum supercomputer to accomplish the task.
Lyoko was later adapted to serve as a sanctuary for him and Aelita. This seems to be a result of his suspicions that someone was watching him. He split the Keys to Lyoko between himself and Aelita, which would make the pair the absolute masters of Lyoko. The government eventually found him, forcing him to flee to Lyoko with Aelita.
Upon reaching Lyoko, Aelita and Franz were attacked by X.A.N.A.. Franz had tried to reason with X.A.N.A., but was unsuccessful. As a last-ditch attempt to stop X.A.N.A., Franz shut down the supercomputer, and it remained that way for one whole decade. Once it was reactivated by Jeremie, X.A.N.A. took control and used it to attack the real world.
After his escape from the supercomputer at the end of Season 2, X.A.N.A. deleted Lyoko's sectors 1 after the other by possessing Aelita and forcing her to enter the Code: X.A.N.A. in each Sector's way tower. At the end of Season 3, X.A.N.A. possessed William and used him to destroy the Core of Lyoko. The Core's destruction resulted with Lyoko collapsing in upon itself, leaving only a X.A.N.A.-possessed William in his wake. Franz Hopper, who managed to escape Lyoko's destruction, was able to send a coded message to Jeremie and Aelita with instructions on how to restore the entirety of Lyoko.
In Season 4, X.A.N.A. still kept attempting to destroy Lyoko after its restoration, and attempted to sabotage the team anyway possible in order to prevent them from catching up with his plans. When recreating Lyoko, Jeremie and Aelita deleted the keys from Sector Five and added a hangar for the Skidbladnir. X.A.N.A. later met his doom at Lyoko as Jeremie launched a program that could destroy him once and for all.
However, X.A.N.A returned mysteriously and because of keeping the Supercomputer shut for a long time, the Lyoko Warriors found out that both the Forest and Ice Sectors had disappeared. The towers of Lyoko have also gained a new appearance in the new season.
Because those on Lyoko are digital rather than organic, they do not age. A clear example of this is given with Aelita, who spends a decade on Lyoko after arriving there around the age of 12. She does not age at any point during those 10 years, though her voice and intelligence change significantly in her slumber.
According to Jeremie's explanation of the 5 Senses in Cruel Dilemma, those on Lyoko have 2 of the 5 Senses: Seeing and Hearing. However, other episodes have shown that Odd, Ulrich, and Yumi have the other three senses (taste, touch, and smell) to a certain degree.
The towers serve as data processing nodes for the supercomputer, and as a link between Lyoko and the real world. By infecting these towers (usually one at a time, but sometimes more) X.A.N.A. can attack the real world. Aelita, Jeremie, and Franz Hopper can operate the towers in the same manner, but not anywhere near as fast and skillfully as X.A.N.A. can. X.A.N.A. can take over towers activated by Jeremie, and Franz can do the same with both Jeremie's and X.A.N.A.'s towers. Aelita is capable of deactivating any activated tower by entering the Code: LYOKO, in the interface inside a tower.
Throughout the four main Sectors, giant wires wind their way out from the 5th sector to each of the towers in each of the Sectors, acting as conduits for data. Red energy can be seen pulsing through these wires whenever X.A.N.A. activates a tower, and pulsations follow the wires along the ground. These wires can be severed.
In Code Lyoko Evolution, Odd, Ulrich and Yumi are now also capable of using towers as long as they have their source codes.
Sectors of Lyoko
True to its name, the Ice Barrier (also known as the "Glacier Region" or "Polar Region" in Season 1) is cold and icy. Composed of large glaciers and thin paths covered in a thin layer of snow, the Ice Sector is just as slippery as any ice-covered area in the real world. While not dark, there is no visible sunlight in this region. Many of the towers in this sector are only accessible through various caves and tunnels, which sometimes forces the group to slide through the tunnels to reach their destination. Additionally, in the episode The Girl of the Dreams, Odd mentions that Aelita may be "in a storm or snowbound," referring to a blizzard, but this phenomenon has yet to be observed in any episode.
Simulated water (not to be confused with the Digital Sea) exists in this sector, and like actual water, can be swum through. X.A.N.A's monsters have proven to be less than proficient swimmers, as 4 Tarantulas drowned in the Temptation. Odd on the other hand has no trouble swimming through the water in Vertigo. With enough speed, Ulrich can run across the top of the water.
This is the only sector X.A.N.A. was unable to delete in Season 3. Though he manages to possess Aelita to do so in an episode prior, it is Aelita herself who willingly deletes it in a Pyrrhic victory in Sabotage so Jeremie could repair the supercomputer.
After X.A.N.A's death and mysterious return, it was revealed that the Ice Sector had disappeared.
The Desert (like any desert worth its name) is dry and sandy as far as the eye can see. It has an oasis, but the water stored there is just an illusion. It leads to a lower platform. The biggest danger is falling off the edge (plateaus are rather small here) and into the digital void below. The Desert is very sunny, reflecting the bright and dry climate of regular deserts.
X.A.N.A. has the ability to create sandstorms in this sector (only seen in Log Book), as well as tremors that cause the plateaus to break apart. Additionally, in Plagued, X.A.N.A. was able to tilt a plateau to a 90 degree angle. Aelita, Odd, and Ulrich were on the plateau at the time and would have fallen into the digital void had Aelita not used her Creativity to save them. The Krabes were able to traverse the tilted plateau easily thanks to their scythe-like legs.
Megatanks are the least proficient in this sector, as their high speed causes them to fall from the plateaus in this Sector. However, the craggy rocks in this sector enable them to easily wage a sneak attack.
Mystery reigns in the enchanted-looking Forest. Graceful trees, suspended in mid-air, let their roots dangle into the void. The Forest can be considered the most beautiful of the 5 Sectors. It also has narrow paths rather than plateaus, though the chance of falling into the void here is less than in the Desert. Despite that, this is not the only Sector where someone has actually fallen into the void. Yumi has fallen in the void in Cruel Dilemma.
The trees also provide excellent cover, which can lead to traps. Like the Ice Sector, there is simulated water in this sector, but in a much smaller quantity. The Forest is typically bright, but not as much so as the Desert. The Forest noticeably changes in the transition between Seasons 1 and 2. In the Season 2, it is far brighter than before, appears to have more trees, and has larger land masses than it previously had. Throughout the series, the Forest Sector serves as the center of Lyoko's plot-related events. In an episode a tower was in the middle of some simulated water. However, this was never shown again.
After X.A.N.A's death and mysterious return, it was revealed that the Forest Sector had disappeared.
Its peaks craggy and its stones sharp, one false move in the Mountain and the group will topple off the rocks into the gaping void beneath. The Mountain is full of moving platforms and tricky obstacles, and is known for having further platforms underneath the "cloud cover," obscuring the digital void in some areas. These clouds make it difficult to aim oneself onto the lower plateaus. X.A.N.A. can extend and thicken the fog. If one of the warriors falls a sufficient distance, regardless of whether or not they land properly, 20 life points are lost on impact. Though not dark, no sunlight is visible in this sector, as the cloud cover obscures it. This is the last Sector to be deleted in Double Trouble.
Being mostly empty sky, the Hornets have the advantage over the group in this sector. In contrast, the narrow paths discourage the use of Megatanks in this sector, since falling off of the edge is quite easy. However, the Megatank's attack makes them effective blockades on narrow paths, since one Megatank can effectively cover a tower on its own without having to worry about retaliation. This is the 2nd and last Sector to be turned invisible in Tip-Top Shape and because of this, Yumi almost fell into the digital sea.
Sector Five (commonly called Sector 5) is a sector hidden deep within Lyoko, first discovered in episode 2 of Season 2. Sector Five is accessible by the special password SCIPIO (from Scipio Africanus, who defeated Hannibal of Sector Five in 202 B.C.). This summons the Transport Orb to the edges of the other sectors furthest from Sector Five to carry its passengers to the Sector's core, called the arena. In the end of "Double Trouble," Jeremie developed a program allowing him to virtualize the warriors directly into Sector Five. Sector Five is the very core of Lyoko itself, with only 1 normal tower instead of the standard 21.
The Sector itself is shaped as a giant blue sphere. On the outside surface of the sphere is a barrier covered with images of binary code similar to those seen in the towers. Floating in the middle of the Sector is the main body of Sector Five — a smaller, but still massive, blue orb. 4 data streams feed from equidistant points on its surface to the 4 other sectors. Everything in Sector Five is blue and geometrically shaped. In this Sector, the digital void has been replaced by a data barrier similar to the ones in the towers, but falling into it seems to be just as bad as falling into the void.
The interior of the orb is an ever-changing maze, designed to act as a security feature to prevent intruders from finding their way around. The interior rooms and corridors of Sector Five are composed of planes, cubes, and rectangles that can slide freely over, around, and against each other. Therefore, this Sector can reconfigure its topography at will.
Upon accessing Sector Five, the labyrinth will reconfigure into a random pattern and a 3-minute countdown will begin, allowing whoever enters to try and traverse the labyrinth and disable the security system. The security system is disabled by pressing a X.A.N.A.-Eye shaped switch (called a "key") somewhere within Sector Five. Like the rest of the Sector, the key is moved with each visit. Failure to deactivate the security system results in the users being trapped in Sector Five and having to wait on someone else to reset the maze from the arena. They do have about a minute or so to escape before this happens though. After recreating Sector Five, Jeremie removes this system, allowing free access to the Sector.
After the security system is shut down, a pathway out of the maze opens up. This leads to a multi-directional elevator. It only stops at one point, so a carefully-timed jump is needed to board it. The elevator moves on tracks around the outer surface of the sphere. It will eventually pause to allow its passenger(s) to disembark. It always pauses at the same spot; another platform that leads to the outer surface of Sector Five. On the surface is a special interface that allows full access to the supercomputer, Lyoko, and X.A.N.A.'s data. While the interface is being used, the user controls in the lab are locked out.
Leaving the Sector can be achieved 1 of 2 ways: the users can either head back to arena and take the Transport Orb or they can head to the surface and wait for Jeremie to open one of the data streams. The 1st option allows the user(s) to be dropped off anywhere in Lyoko. The 2nd allows them to exit through an exit tower in the sector that corresponds to the data stream they use. Since the towers are destroyed in Season 4, the gang ends up outside of a giant hole outside of Sector Five.
Within this Sector are unique monsters that call it home. The first of these are the Creepers. These monsters never leave Sector Five. They aren't very tough, but possesses powerful lasers and can scale the walls of the sector as if they were walking upright. Another are the Mantas. They usually hatch from the outside surface of the Sector to prevent intruders from leaving, but have traveled to other Sectors on occasion. The last is the Scyphozoa. Unlike the other monsters, the Scyphozoa is nearly (if not completely) invincible. To date, it has only been destroyed once. There seems to be only one throughout the show. This monster's main purpose is to steal memories, usually Aelita's. It first appeared in Sector Five, but now travels wherever it is needed. No other monsters appear in this Sector, likely due to its unique layout and purpose.
Sector Five is the only Sector which can actually devirtualize the heroes without the help of monsters. Various traps exist in this region that can remove a hero in 1 or 2 hits. One such set of traps are the walls and ceiling of Sector Five, which can easily be moved into positions that will flatten the heroes. Pieces of the ceiling can also be shaken loose, producing the same, albeit less-controlled, effect. As one would expect, getting flattened automatically devirtualizes them. Odd has been the victim of this trap the most; he compares the experience to being run over by a steamroller. Another less-common trap are security lasers. These have only appeared in "Exploration" and when Yumi lost 90 life points of damage in a single hit.
This Sector is not connected to the regular materialization program, which means that if the characters lose their life points here, they will not automatically return to Earth unless the proper program is run. In "Exploration," Aelita was forced to sort through the data contained within the Sector in order to find the proper materialization program.
This Sector was the 1st Sector to exist, even though it's classified as the 5th. As described by Franz Hopper, the original Project Sector Five seems to be represented by this Sector, even though the project existed before the Supercomputer did. Its purpose was to disrupt enemy communications. For a reason that has yet to be revealed, Hopper sought the destruction of this place. To that end, he designed the supercomputer, Lyoko, and X.A.N.A. to destroy it. He never went through with this plan, though. Instead, he reworked the rest of Lyoko to serve as a sanctuary for him and Aelita. When they were finally forced to travel there, X.A.N.A. rebelled. It isn't clear why he did so, but it is clear that X.A.N.A. took control of the Sector instead of destroying it as Hopper had intended.
Within the heart of Sector Five lies Lyoko's core, the code which maintains the virtual world. Should it be
destroyed, Lyoko and anyone on it would go with it. The core is suspended near the top of Sector Five's inner chamber by three conduits. The core itself is a miniature version of Lyoko. Surrounding the core are two transparent cubes, both of which act as shields. A large amount of sustained laser fire is required to break through them. Since these shields regenerate with each failed attempt to destroy the core, destroying it takes a long time. The core is only accessible through a passage on the bottom of Sector Five, and the passage is protected by a door that rapidly alternates between open and closed. A key similar to the one that shuts off the timer is present just past the door, and produces a staircase into the actual room.
The dock for the virtual ship Skidbladnir is later created in a similar location, and even has an elevator to access it. This elevator, however, stopw at point points for easy access. In addition, the dock is located near the top of the huge glowing white orb.
Seen only twice (once in Frontier and again in Jeremie's dream in Code: Earth), the virtual limbo exists as a null space between Lyoko and the real world. It exists within the Supercomputer's memory, which Aelita is linked to. Jeremie was accidentally trapped here when he 1st attempted to go to Lyoko. The scanner memory had been cut off before the process had completed, trapping him in the limbo.
Upon his arrival, Jeremie was able to speak to Aelita through her link to the Supercomputer's memory. Through the link, Jeremie was able to tell the others how to free him. After traveling to all 4 regions and collecting the scanner memory from all 4 passage towers in Season 1, Aelita was able to travel into the limbo and free him. During that time, their minds were connected, which allowed them to sense the other's very thoughts, emotions and feelings.
The Digital Sea is random data floating about the network that looks and moves like water, hence the name. It lines every Sector in Lyoko, with the exception of Sector Five, which is lined with an equivalent data barrier. Falling into the sea causes permanent devirtualization, reducing a person to data that is pulled through the network at random. Monsters on Lyoko are destroyed when they impact the sea, producing a large column of energy. Jeremie can track down those people who are lost and use his materialization program to recover them, but he still doesn't recommend falling in since finding them is a difficult task. Yumi is the one of those that has ever fallen in (in Cruel Dilemma), and she was recovered shortly after, though only barely and Jeremie was only able to save her because Odd had inadvertently entered the proper code earlier (by dropping candy on it), creating a one-time materialization program. Aelita has fallen into the Digital sea once (in Distant Memory). However, she was saved by Franz Hopper, who manifested himself as a glowing ball of pure energy.
In Season 4, X.A.N.A. William could come and go through the sea as needed. Later, Jeremie decides that the best way to find X.A.N.A. is to search the digital sea. To that end, he creates a specialized vehicle dubbed Skidbladnir (after the Norse ship of legend) to explore it. The Digital Sea resembles a large upside-down city, the "buildings" presumed to be networked databases by Aelita. Various network "hubs" are anchored to the city by glowing blue tubes, allowing for near-instantaneous travel across large distances in the network. X.A.N.A. even has monsters inside the digital sea, such as the Kongres.
Also floating within the sea are specially-designed "Replikas" of Lyoko, created by X.A.N.A. from the data he had stolen from Aelita (Presumably in The Key). Each Replika consists of a single Lyoko sector, and is powered by its own Supercomputer in the real world. Jeremie's plan throughout most of Season 4 is to find a way to destroy the X.A.N.A.-built Supercomputers by creating a method of materializing the group's Lyoko powers into the real world.
In "Rock Bottom?", it is stated by Aelita that Lyoko is constantly changing its position on the Network, meaning either different parts of the Digital Sea flow into it at different times as it drifts across the Internet, or that Lyoko isn't actually housed in the Supercomputer at all, but is instead run as a sort of server on the Internet managed by the Supercomputer.
Xanadu is what Lyoko was called when it was being pitched in Garage Kids. It looked most like the Forest Sector in design, but there are several major differences that distinguish it from the main series' Lyoko. Xanadu was much smaller than Lyoko, however, and there were towers of varying sizes and widths. Aelita was not present. Under Xanadu's model, monsters would attack towers, causing damage to the real world. The avatars were very different as well.