Editing Code Lyoko (section)

== Plot ==
Jeremy Belpois, an 8th grade prodigy attending boarding school at Kadic Academy, discovers a quantum [[supercomputer]] in an abandoned factory near his school. Upon activating it, he discovers a virtual world called Lyoko with an [[artificial intelligence|artificially intelligent]] girl named Aelita trapped inside it. He also finds out about X.A.N.A., a fully autonomous, malevolent, and highly intelligent [[multi-agent system]], that also dwells within the Supercomputer. Using Towers on Lyoko to gain access to the real world, X.A.N.A. can possess electronics and other targets like a virus to wreak havoc. X.A.N.A. is determined to eliminate anyone aware of the Supercomputer's existence so it can be free to conquer Earth and destroy all humanity.

Jeremy works tirelessly to materialize Aelita into the real world and stop attacks caused by X.A.N.A., being aided by his three friends, Odd Della Robbia, Ulrich Stern, and Yumi Ishiyama, who are virtualized into Lyoko to save both worlds from the evil virus. They achieve this by escorting Aelita to various Towers on Lyoko, which serve as interface terminals between Lyoko and Earth. Once the Tower is deactivated, Jeremy can launch the "Return to the Past" program, which sends the world back in time to undo any damage caused by X.A.N.A., while anyone scanned into the Supercomputer retains their memory of the events. In "Code: Earth," Aelita is finally materialized, but the group discovers that X.A.N.A. had planted a virus inside of her that will kill her if the Supercomputer is turned off. They realize that they cannot destroy X.A.N.A., or Aelita will be destroyed along with it.

In Season 2, Aelita adjusts to life in the real world, while Jeremy attempts to develop an [[antivirus program]] to liberate her from X.A.N.A.'s power. On Lyoko, a fifth sector is discovered and the group explores more of Lyoko's secrets and mysteries. The gang begins to uncover information about a mysterious man named Franz Hopper, who went missing ten years ago. He supposedly created the Supercomputer, Lyoko, and X.A.N.A., and is eventually discovered to be Aelita's father. They finally find out that Franz Hopper is indeed alive somewhere, hiding in the uncharted parts of Lyoko to avoid X.A.N.A. All the while, X.A.N.A. attempts to steal Aelita's memory to gain the Keys to Lyoko and escape to the internet. At the end of the season, the group discovers that Aelita is actually human and does not have a virus, and instead is missing a fragment of herself. In "The Key," X.A.N.A. tricks them with a fake and succeeds in stealing Aelita's memory and escaping the Supercomputer. Aelita appears to perish as a result but is revived when Franz Hopper restores her completely, along with her missing fragment: the memories of her life on Earth before she was virtualized on Lyoko.

Season 3 shows that since succeeding in escaping the confines of the Supercomputer, X.A.N.A. targets the virtual world itself by destroying each of Lyoko's surface sectors, until only Sector Five is left. Initially reluctant, the Lyoko Warriors decide to invite William Dunbar as the sixth member. However, shortly after being virtualized, he is possessed by X.A.N.A. Shortly after, he destroys the Core of Lyoko, destroying the entire virtual world and rendering the group unable to fight X.A.N.A., putting the entire real world in danger. After what they thought was their defeat, Jeremy receives a coded message from Franz Hopper that allows him to recreate Lyoko and continue the fight against X.A.N.A.

In Season 4, Jeremy and Aelita construct a digital submarine, the [[Skíðblaðnir|Skidbladnir]], to travel across the Digital Sea to destroy X.A.N.A.'s "Replikas," which are copies of Lyoko's sectors that are linked to X.A.N.A.-controlled supercomputers on Earth, all created for its goal of world domination. X.A.N.A. uses William as its general throughout the season to defend the Replikas and target the Lyoko Warriors in any way he can. To prevent suspicion regarding William's disappearance, Jeremy manages to program a specter to take William's place at Kadic, although the clone has low-level intelligence and acts very stupidly. Near the end of the season, X.A.N.A. decides to draw energy from all of its Replikas to create the Kolossus, a gigantic monster that later destroys the Skidbladnir. Before Kolossus destroys the submarine, Jeremy frees William from X.A.N.A.'s control. After his return, he has a difficult time gaining the trust of the group. While Ulrich defeats the Kolossus, Franz Hopper sacrifices himself to power Jeremy's "anti-X.A.N.A. program," which destroys X.A.N.A. forever upon activation. Shortly after, the group, albeit reluctant due to their nostalgia, decides to shut down the Supercomputer.