Code Lyoko

After William is initiated into the group, a series of events leaves only him and Aelita to defend Lyoko's core. During William's first mission to Lyoko, Xana uses the Scyphozoa to possess him, making him the general of a massive army focused on Lyoko's core. Despite their best efforts, the group can't stop the possessed William from destroying the core, which both renders the supercomputer useless and transforms William into a darker, Xana-themed version of himself. Later, in the Hermitage, while the group broods over their predicament, Jeremie receives a coded message directly from the internet, sent by none other than Franz Hopper who somehow survived the destruction of Lyoko.

When Odd complains that he doesn't have any cool powers on Lyoko like his friends, Jeremie designs him a teleportation power. It works, but ends up leaving duplicates of himself in the location he teleported from in The Mountain Sector. After trying it twice, Jeremie devirtualizes Odd to find out what went wrong, accidentally creating three clones. Meanwhile, in the real world, Xana attacks using a mysterious smoke that turns anyone it hits to stone. One of Odd's copies gets turned to stone, so the other two Odds must retrieve him before they become unstable and disappear.

When Xana sabotages the supercomputer, weird bugs begin cropping up in Lyoko. With its power rapidly draining, Jeremie needs to repair it before it becomes completely useless. However, he seems to forget about boys' dorm inspection, so Jim forces him to stay behind. Meanwhile, Xana possesses vines to trip up the rest of the group, except Aelita. Since the attack keeps draining power from the supercomputer, Aelita purposefully wipes out The Ice Sector leaving The Mountain Sector left.

After being rejected by Yumi, William makes it his mission to find out the secret she's hiding. Soon enough, he manages to follow Ulrich and Odd to the factory and learns about Lyoko and Xana. Meanwhile in The Ice Sector, the Scyphozoa possesses Aelita to enter Code:Xana in the way tower, but is devirtualized just in time. The group thinks William's help is going to be quite useful, when a possessed demolition worker sets several bombs in the factory. They take a vote as to whether or not to include William as part of their group, but Yumi votes no and Jeremie initiates a return to the past.

Aelita gets mad at Jeremie and she and Odd go into Lyoko without telling anybody, which causes problems. On lyoko, Xana creates a diversion to get everybody to deactivate the tower in The Mountain Sector while the monsters (mostly Mantas and Creepers) worked on destroying the core of Lyoko. Jeremie and Aelita find a strand of DNA that belongs to Franz Hopper, indicating he may be still alive.

Xana attacks the Lyoko warriors by possessing a large amount of food. At the same time, he bugs up The Mountain Sector by rising the digital sea, but Odd and Aelita go to Sector 5 to stop him. Xana also mounts an attack on Lyoko's core at the same time.

After another three-week vacation, the group is still looking for a way to fight X.A.N.A.. X.A.N.A., meanwhile, is trying to destroy Lyoko, preventing them from doing just that. He does so by targeting the core, which contains the code that maintains the virtual world. In a side story, Odd blackmails Jim into asking Principal Delmas to make Odd have the same classes as his friends. Additionally, Yumi decides against having a relationship with Ulrich and decides it would be better if they were just friends. While defending the core, Aelita is suddenly devirtualized by the enemy. However, she still ends up back in the scanners and Jeremy realizes that this is because Aelita is fully human, just like the rest of the group, so she does not need Code: Earth anymore to be materialized on Earth.

After going through all of Franz Hopper's diary, Jeremie discovers the truth behind the supercomputer, at least to some extent. Hopper had used it quite extensively, to the point of repeating a single day for more than seven years. His sanity degraded throughout the experience. Hopper also revealed that he and Aelita hold the keys to Lyoko, which Xana was after. He only needed her half, now. The keys would allow him to escape the supercomputer. Jeremie also finds a way to free Aelita from the supercomputer. It turns out that Aelita never had a virus. In fact, Xana had been holding onto a piece of her, which was responsible for linking her to the supercomputer. Aelita is not willing to go, angry over the fact that Hopper had essentially taken her life from her. She's also worried that Xana might escape. To that end, she shuts down the supercomputer. Jeremie rescues her, and the group goes to Lyoko to retrieve her fragment. After all their efforts, they seem to succeed, but it turns out to be a fake. Xana manages to devirtualize Aelita's defenders and steal her memory, effectively killing her and allowing him to escape, which shuts down Lyoko in the process. His escape allows Franz Hopper to revive Aelita and Lyoko, restoring all of Aelita's memories in the process. Through the restoration, Aelita finally remembers her past up to the point that she went to Lyoko. With Xana now free and Aelita's memories returned, neither are linked to the supercomputer. This means that they could shut it down, but it would do no good. Unsure of how they'll proceed, Jeremie promises that they'll find a way to stop Xana.

During a short film made by Odd and starring Sissi, Sissi seems to be possessed by a ghost. She does not act as expected, however. Instead, she starts speaking in some strange language, focusing on Jeremie as she does. She is taken to the infirmary as a result. Later on, she walks into Jeremie's room and writes some code on a piece of paper. Jeremie translates the code, revealing a message stating a desire to help. Sissi is sent to the hospital after this, forcing Odd and Yumi to go there and collect her. On a trip to Lyoko, Aelita and Ulrich discover a white tower. Xana isn't happy about the tower, and sends Megatanks to shut it down forcibly. At the same time, it activates a tower and possesses a nurse at the hospital to do the same to Sissi. Odd and Yumi are able to prevent the nurse from doing so. They bring Sissi to the factory to finish the message she started earlier. She manages to type most of it out before Xana succeeds in shutting down the white tower. After Xana's tower is shut down, Jeremie translates the message, revealing that Franz Hopper had activated the white tower.

After reading about a dead man named Leon Corbe, who died during the construction of Kadic, Sissi decides to hold a séance to communicate with him. She manages to convince Ulrich to attend. During the séance, one of Xana's ghosts appears in the form of a four-armed monster. At first, it seem docile, but quickly gets angry and attacks. Ulrich leaves Sissi with Odd while he goes to tell Jeremie. Jeremie can't find an activated tower, which seems wrong considering the situation. As Jim patrols the hallways, he is picked up by an invisible object. Jeremie, Odd, and Ulrich arrive to spray it with a fire extinguisher, confirming that it's a ghost and implying that the super scan is broken. With the ghost on the loose, the group heads off to the factory. After they arrive, Aelita, Odd, and Yumi head to Lyoko. Odd looks for the tower while the other two head to The Carthage Region to fix the super scan. Meanwhile, Jeremie and Ulrich are left to deal with the ghost.

Aelita's visions become a problem once again, but not the same visions as before. This time, she has visions of her and Franz Hopper being chased by government agents. The visions come even when she's awake, causing her to lose consciousness while at the pool. Wanting to know the source of the visions, she heads to the Hermitage to learn more about them. Jeremie discovers that Xana is causing the visions through her link to the supercomputer. During the mission to stop them, Aelita breaks away and heads to The Carthage Region, determined to discover the source of the visions.

After a trip to the Carthage Region, Jeremie believes he has the data necessary to cure Aelita's virus. While the two work on the cure, Odd, Ulrich, and Yumi go to a rock climbing contest. Odd races against Hervé, who is no match for Odd. William then goads Ulrich into racing, despite his obvious reluctance. During the race, Ulrich gets dizzy and falls. Yumi realizes that he must have vertigo. Ulrich, embarrassed, runs off. Meanwhile, Jeremie finds the anti-virus and gives it to Aelita. Despite some problem with the application, it seems to work. However, this does not last. An error in the anti-virus causes her to turn invisible. On top of that, she can't enter the towers on Lyoko, making it impossible for her to stop Xana's latest attack, which is a possessed pack of wolves targeting Odd, Ulrich, and Yumi.

After a malfunction and a little bug with the regular materialization program, Odd and Yumi are bugged up, ending up in each others' bodies. Even worse, their atoms start splitting after a while due to being dematerialized, even on Lyoko. The gang has to go to Lyoko and fix the problem before Odd and Yumi disintegrate and disappear forever, but it's not easy when Xana tries to stop them.

When Xana possesses Kiwi, it turns the little dog into the carrier for a virulent virus that turns those it infects into zombies. To make matters worse, Aelita and Jeremie are stuck in the cafeteria and can't get to the factory. On top of that, Odd is a zombie himself. Jermie and Aelita escape but Ulrich and the other students (except William, who is turned into one himself) fight the rest.

After a Xana attack, Jeremie insists on a return trip, regardless of the fact that Xana didn't even cause any damage. When questioned, he gets defensive and angry, insisting that it's necessary. Further questioning on the matter leads to the same result. After the next return trip, Jeremie is found unconscious in his room. Yumi and Ulrich go searching through Jeremie's room to see what they can find about Jeremie's problem. Upon decoding a video diary that is stored on his computer, they learn that he had been using the return trips to increase his own intelligence. When he's about to be taken to the hospital, Xana attacks, possessing the ambulance and driving it towards the river with Yumi with him. Now the others have to save Jeremie and deactivate the tower without Jeremie's help.

After deciphering a part of Franz Hopper's diary, Jeremie gets an idea to make a monster that fights on the side of good. By combining techniques, he makes the Marabounta, a sphere that can replicate itself endlessly and devour any monster it can encase. Though it works quite well to begin with, everything goes wrong when it senses Aelita's virus, which is linked to Xana. After Odd attacks it to save her, the Marabounta goes haywire and threatens to devour all of Lyoko, so XANA sends his monsters to help destroy the Marabounta in order to protect Aelita and her memories. The monsters leave the Lyoko Warriors without causing any trouble.

During a mission to The Carthage Region, the Scyphozoa attacks Yumi, stealing her human DNA, having her trapped on Lyoko. To make matters worse, it's picture day for her class and she will be suspended if absent. After some discussion, Ulrich gets the idea to have Sissi stand in for Yumi. Strangely, Sissi agrees and asks for nothing in return. During this, Jeremie tries to come up with a way to bring Yumi back. Aelita thinks of a way, but won't tell Jeremie about it. She only tells him once she gets to Lyoko, so he can't object. She begins to transfer her own genetic code to Yumi, which will let Xana take her memory at will, being exposed. Luckily, Odd and Ulrich get there in time to stop her. Meanwhile, Jermie figures out that Yumi's DNA should be stored in XANA's memory, which is accessible through Sector Five.

It's Saint Valentine's Day and love is in the air. Ulrich forgets, so at last minute writes a poem for Yumi. However, when William presents Yumi with flowers, Ulrich gets jealous and reads the poem to Sissi instead, hoping to elicit jealousy from Yumi. The two end up in a fight, both bothered and wondering if the other really likes them. Also, a man possessed by Xana leaves a necklace at Aelita's door, Aelita is convinced that it was Jeremie who got it for her. Since Jeremie didn't actually get it, he's left to wonder who did, and ends up suspecting Odd, who avoids the question. This puts the two at odds, so to speak. Meanwhile, Aelita's necklace takes control of her and forces her to deliver herself to the Scyphozoa. Luckily, Odd arrives in time, and is able to save Aelita from the Scyphozoa by "threatening" to kill her.

After taking another trip to The Carthage Region and returning to the school, Aelita talks to Jeremie about not being human, unaware that Sissi is recording their conversation. On top of that, the data they had retrieved from the Carthage Region takes over the supercomputer and starts running return trips over and over. Jeremie discovers that returning to the past makes X.A.N.A. much stronger and more powerful. During the third return trip, Xana possesses Sissi with his newly strengthened and increased abilities and powers and goes after Ulrich. Not only does the group have to deal with Sissi, but they also have to stop the return trips from continuing.

While Aelita adjusts to her new life on Earth, Jeremie and the others investigate the mysterious owner of the Hermitage, Franz Hopper, and his link to the supercomputer, Lyoko, and Xana. It is discovered that Franz Hopper was in fact a former teacher at Kadic. After being teased by Sissi, Aelita retreats to Lyoko but gets lost. Jeremie finds her in a previously undiscovered fifth sector of Lyoko, The Carthage Region.

Aelita is materialized, but unfortunately, Xana implanted a virus inside of Aelita, so if Xana dies, so does Aelita. Then Xana decides to attack with bringing his own monsters to Earth. Ulrich and Yumi fight off the monsters, while Odd goes to Lyoko with Aelita. Odd eventually get materialized himself, but luckily, Ulrich and Yumi reach the factory, and fight off the last Hornet, attacking Aelita. She deactivates the Tower, and on the second run, the gang is talking with Aelita, about finding an anti-virus, but Aelita can still be materialized for small visits. So they look ahead to the future, and the episode ends.

One day at school, Jeremy notices that Odd, Ulrich, and Yumi are missing. Meanwhile, Odd, Ulrich, and Yumi ARE at school with Jeremy! What's going on? Turns out that XANA (in the form of Jeremy) has trapped Odd, Ulrich, and Yumi in a virtual world identical to the boarding school, completely at his mercy. With Aelita's help, Jeremy reaches the fake school and tries to convince his friends that he is the real Jeremy and that the imposter is XANA. When they learn that Jeremy got into the scanner to come here, XANA claims that Jeremy is the fake because he would never go into the scanner. But the others say that if his friends were in danger, he would. XANA gets angry and tries to crush everyone with wires and holographic zombies of Jim, Nicholas, and Herve. But Aelita destroys the false school just in time, foiling XANA's plan.

Ulrich is getting tired of getting being rebooted so many times and waiting to find out if Yumi has feelings for him or not. He thinks these are his only troubles, but he is not counting on two things: 1) Sissy getting in the way again and 2) Xana's latest attack which is quite deadly. He disconnects the scanners that makes the return to the real world if he or any of the gang lose all their life points. Instead of returning devirtualized, they could die in Lyoko. Can Aelita shut down the tower in time?

Both Herb & Jeremy are in a robot competition Herb with ""Iron Sissy"", and Jeremy with ""Kiwi 2."" Herb cheats by launching a gear from Sissy to destroy ""Kiwi 2."" Meanwhile, Xana's latest plan, using the factory to built a robot. Ulrich & Yumi get help from Herb in slow down Xana's robot. Jeremy discover that Xana robot had built in the factory and messed with computer that goes to Lyoko. Jeremy fixes the super computer, and Odd helps out Alieta in Lyoko. After the time reboot, Kiwi 2 dodges Herb's gear to win the contest.

A new rock song Odd downloads sends him into a coma, and the same song is passed through the school. XANA's new beat is the cause, and he can broadcast it anywhere. The hospital is full to bursting with cases, and Odd's heart gets weaker with every beat it makes. But when the tune starts playing in the factory, will the crew learn that music can do more than just soothe the soul? And, will Aelita be able to save the crew? It's all up to a leap of faith...

After a quick game of soccer, Yumi heads home for the night, but Odd and Ulrich head in for dinner, and Jeremie is already there. He decides to check on Aelita, and Yumi ends up following him instead. But, while scarfing the desserts the others left behind, he and Ulrich get caught up in a shocking Xana trap. Not only is the lunchroom electrified, the roof may fall in at any time. Even the combined power of the eight kids trapped inside - including Odd, Ulrich, and Sissy - can only delay Xana for a short time. Will Yumi be able to get Aelita to the tower before the room becomes a final resting place for our heroes?

It's the anniversary of the day Jeremie and the others met Aelita. They begin planning a surprise for her, unaware that Sissi is spying. When Jeremie and Odd try to open the lab elevator, it won't work. They go to the control room to see what's wrong and XANA uses the machinery in the room to attack them. They escape and reach the lab basement. Meanwhile, Ulrich and Yumi get to the elevator. This time it opens. Sissi gets in with them at the last moment, but just then XANA causes the elevator to plummet down the chute. Yumi escapes to go join Jeremy and Odd in the lab. Back at the elevator, water leaks from the walls and begins to drown Ulrich and Sissi. Ulrich promises that if they get out alive, he'll be nicer to Sissi. Aelita manages to input Code Lyoko and reset time just Ulrich and Sissi begin to drown. At the end, Jeremie and the others present Aelita with an anniversary cake and Ulrich keeps his the promise he made to Sissi in the elevator.

Ulrich is fussing over a mysterious letter found slipped under his door one night... a love letter signed by Yumi! Meanwhile, XANA infects a hive of bees and is using it to attack our heroes. Ulrich struggles with his feelings and how to tell Yumi how he feels about her; that is, if he can figure it out himself, and saving the day from XANA in an episode of life and death.

Jeremie mysteriously loses contact with Aelita. The same day, a new student named Taelia (who looks alot like Aelita) arrives at school. Jeremie is convinced that Taelia is Aelita devirtualized, but the others aren't too sure. Meanwhile, XANA posseses an ancient samurai armor that Yumi brought for a project and goes out to kill Jeremie and the others. Jeremie heads to the lab, taking Taelia with him, hoping that she'll get over her ""amnesia"" and remember that she is Aelita. But what happens when Jeremie discovers that he wrong?

When a director comes to town to film a movie, XANA posseses a plastic alien model in order to destroy Ulrich and the others.

Jeremie is working on the materialization program, and finally gets it. Jeremie wants to matierialize Aelita, but realizes that preparations need to be made. That night, Xana possesses two bulldozers and starts to destroy the factory. Odd and Yumi go into Lyoko where she falls into a virtual black hole. In order to save Yumi's life, Jeremie has to choose between either materializing her or Aelita.

Sissi has found something very special and dear to Ulrich, his diary! Unfortunately the diary contains some information on X.A.N.A. and Lyoko. Sissi decides to use this as a means of blackmail to get with Ulrich. Later Odd, Ulrich, Sissi, and some of the other students are going to a pool, the bus that their riding in is X.A.N.A.'s next target. He wants to ram the bus into a chemical plant. Now the team must head to Lyoko to help Aelita get to the tower to save the students and the rest of the city.

Odd decides to start a music band with his friends. But Jeremy can't play, so they try to hire a drummer. In the end, the best drummer they can find is Nicholas (Sissi's blond-haired crony). As the group argues over whether or not to let Nicholas join the band (Ulrich and Yumi: Pro-Nicholas. Odd: Anti-Nicholas, Pro-Naomi), Jeremie alerts them that XANA is planning to overload a pylon and send this massive electric current through the telephone wires to blow up a nuclear power plant. Just in the nick of time, Aelita, Ulrich, and Odd stop XANA's plan. At the end of the episode, Odd gives in and allows Nicholas to be the drummer of his rock band.