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The fourth season of Code Lyoko originally aired from May 18, 2007 to November 17, 2007. It mainly focused on the group traveling the Internet in search of X.A.N.A., in their virtual submarine: the Skidbladnir. Using their ship, they go searching for Replikas to destroy them to prevent X.A.N.A. from succeeding in world domination. They also try to rescue a X.A.N.A.-fied William and bring him back home.


Recreating Lyoko and the Return of William[]

William possessed

William returns as X.A.N.A.'s loyal minion

After the Core of Lyoko is destroyed, the group searches for a way to rebuild Lyoko once more so they can travel through the web. After a long summer, Jeremie and Aelita announce that they have successfully rebuilt Sector Five. The group also discusses William and how he was lost in the Digital Sea after Lyoko was destroyed. However, Jeremie has a trick up his sleeve and calls the principal to inform him that William would not be returning to Kadic Academy anytime soon. However, to add to the mystery, William unexplainably returns. This was simply a plot by X.A.N.A. to capture and kill Aelita. After a brief battle, the group discovers that William is almost permanently X.A.N.A.-fied and they must rescue him. (William Returns)

The Skidbladnir[]

Skid hangar

The Skidbladnir in the middle being fully constructed.

Since X.A.N.A. is now scattered around the internet, the team is now facing to how to directly counter X.A.N.A. As Jeremie works around the clock to find a solution, he finally comes up with the idea of a virtual submarine, named the "Skidbladnir". X.A.N.A. attempts to destroy the ship before it is fully completed, but fails while trying ao. However, he is able to steal some data which would be later used to program William's own mini-submarine called Rorkal. (Skidbladnir)

Battle of the Replikas[]

Premier voyage 293

The Lyoko Warriors discover the Forest Replika.

With the Skidbladnir all programmed and ready to go, the Team decides to hunt down X.A.N.A. on the network as to bring William and Waldo Schaeffer home. During the maiden voyage, the team stumbles upon an an unknown sphere. However, the team later realizes that this was not in fact Lyoko. (Maiden Voyage)

They later return to this mysterious sphere and realize it is an exact copy of Lyoko, except that instead of housing four sectors, it houses just one. (Replika)

These "Replikas" are housed the same way as Lyoko is: inside a supercomputer. After this discovery, Jeremie finds a way to bring them to the real world as spectres to destroy supercomputers that house the Replikas. (Lab Rat, Bragging Rights, A Lack of Goodwill, Hard Luck, A Space Oddity, Cousins Once Removed, Cold Sweat, Down to Earth)

Return of Franz Hopper[]

Franz Hopper Orb

Franz Hopper.

Waldo Schaeffer (also known as Franz Hopper) makes his first re-appearance after Aelita is thrown into the Digital Sea. He saves Aelita, and also provides Jeremie with some data before disappearing once again. (Distant Memory)

Schaeffer appears for the last time in the penultimate-episode. He provides Jeremie with data that could potentially destroy X.A.N.A. (Fight to the Finish)

Demise of Franz Hopper and the Annihilation of X.A.N.A.[]


The Multi-Agent program in a working state.

With the data finally accessible, Jeremie programs the "Multi-Agent Program" which can destroy all of the Replikas and X.A.N.A. himself. However, there was not enough power available. As Mantas were attacking Franz Hopper, he offered the power to utilize the program.

Just as the program began to run, he was permanently devirtualized. X.A.N.A. was wiped out along with the Replikas, with the cost of Waldo's own life as well. (Fight to the Finish)

List of Episodes[]

Ep No. Pro No. Name Image French Title Airdates
1 (66) 401 William Returns
66 william returns
Renaissance US: May 18th, 2007
FR: August 13th, 2007
2 (67) 402 Double Take
67 double take
Mauvaise réplique US: June 12th, 2007
FR: August 14th, 2007
3 (68) 407 Opening Act
68 opening act
Première partie US: June 19th, 2007
FR: August 30th, 2007
4 (69) 405 Wreck Room
69 wreck room
Double foyer US: June 26th, 2007
FR: August 15th, 2007
5 (70) 403 Skidbladnir
70 skidbladnir
Skidbladnir US: July 3rd, 2007
FR: August 16th, 2007
6 (71) 406 Maiden Voyage
71 maiden voyage
Premier voyage US: July 10th, 2007
FR: August 17th, 2007
7 (72) 410 Crash Course
72 crash course cut
Leçon de choses US: July 17th, 2007
FR: August 20th, 2007
8 (73) 412 Replika
73 replika
Réplika US: July 24th, 2007
FR: August 21st, 2007
9 (74) 409 I'd Rather Not Talk About It
74 I'd rather not talk about it
Je préfère ne pas en parler US: July 31st, 2007
FR: August 22nd, 2007
10 (75) 413 Hot Shower
75 hot shower
Corps céleste US: August 23rd, 2007
FR: August 14th, 2007
11 (76) 404 The Lake
76 the lake
Le lac US: August 21st, 2007
FR: August 24th, 2007
12 (77) 408 Lost at Sea
77 lost at sea
Torpilles virtuelles US: August 28th, 2007
FR: August 27th, 2007
13 (78) 414 Lab Rat
78 lab rat (experience in french)
Expérience US: Unaired (Aired Online)
FR: August 28th, 2007
14 (79) 415 Bragging Rights
79 bragging rights
Arachnophobie US: September 8th, 2007
FR: August 28th, 2007
15 (80) 416 Dog Day Afternoon
80 dog day afternoon
Kiwodd US: September 15th, 2007
FR: August 29th, 2007
16 (81) 420 A Lack of Goodwill
A Lack Of Goodwill Title
Œil pour œil US: September 22nd, 2007
FR: August 30th, 2007
17 (82) 422 Distant Memory
82 distant memory
Mémoire blanche US: September 29th, 2007
FR: August 31st, 2007
18 (83) 421 Hard Luck
83 hard luck
Superstition US: October 6th, 2007
FR: September 8th, 2007
19 (84) 411 Guided Missile
84 guided missile
Missile guidé US: October 13th, 2007
FR: September 15th, 2007
20 (85) 417 Kadic Bombshell
85 kadic bombshell
La belle de Kadic US: November 3rd, 2007
FR: September 22nd, 2007
21 (86) 419 Canine Conundrum
86 canine conundrum
Kiwi superstar US: November 10th, 2007
FR: September 29th, 2007
22 (87) 423 A Space Oddity
87 a space oddity
Planète bleue US: November 17th, 2007
FR: October 6th, 2007
23 (88) 427 Cousins Once Removed
88 cousins once removed
Cousins ennemis US: November 17th, 2007
FR: October 13th, 2007
24 (89) 418 Music to Soothe the Savage Beast
89 music to soothe the savage beast
Il est sensé d'être insensé US: Unaired (Aired Online)
FR: October 20th, 2007
25 (90) 425 Wrong Exposure
90 wrong exposure
Médusée US: Unaired (Aired Online)
FR: October 27th, 2007
26 (91) 428 Bad Connection
91 bad connection
Mauvaises ondes US: Unaired (Aired Online)
FR: November 3rd, 2007
27 (92) 424 Cold Sweat
92 cold sweat
Sueurs froides US: Unaired (Aired Online)
FR: November 3rd, 2007
28 (93) 426 Down to Earth
93 down to earth
Retour US: Unaired (Aired Online)
FR: November 3rd, 2007
29 (94) 429 Fight to the Finish
94 fight to the finish
Contre-attaque US: Unaired (Aired Online)
FR: November 10th, 2007
30 (95) 430 Echoes
95 echoes
Souvenirs US: Unaired (Aired Online)
FR: November 10th, 2007


During production of Season 2, Code Lyoko was renewed for 45 episodes.[1][2] Initially it was planned to split the episodes between two seasons of roughly 22 episodes each.[1] As the plot following X.A.N.A.'s escape from the supercomputer was coming together, the writers envisioned an ambitious story involving the exploration of the Digital Sea, new 2D and 3D outfits for the heroes, and creating new locations in 2D for the heroes to teleport to in their Lyoko forms and do battle.

Due to the scale of the story and the large number of episodes, the writers had to compromise with the producers regarding the budget. As Jérôme Mouscadet recalled: "This is what we negotiated with the producers, in collaboration with them: we were to do a 15-episodes season with no new creation at all, which inspired Sophie [Decroisette] this great concept of “destroying Lyoko” with disappearing sectors, which was quite awesome, and then we could save a lot more new locations for season 4, and many more things to do. So we used season 3’s development for season 4." While the general ideas and scope were figured out by this point, Season 4's concept was still being worked on while the scripts for Season 3 were being written.[3]

Sophie Decroisette was involved in the early planning for Season 4, working on the story bible and being involved in the early talks regarding Replikas.[4] She said: "In this season, Xana goes on with his plan to take over the world, and we asked ourselves how this would be possible. What he could do to impose his dominance over humans. And we also wanted the heroes to be able to materialize as spectres on earth. [...] These basic ideas resulted in the replikas: Xana was beginning to spread [to other] supercomputers and “other Lyokos” everywhere…". In order for the heroes to transverse the Digital Sea, she drew inspiration from Norse mythologies.[5] She discovered the Skidbladnir ship while researching, and liked it enough to add it to a list of possible names for Mouscadet. They ended up selecting it as they found "Skid" to be a "nice" nickname, which also let them include an illusion to the pilot with the Garage Skid (called the Skid Hanger in the English dub). The decision also allowed the show's designer to draw inspiration from "an existing image" in the words of Mouscadet to "make sense out of things".

Decroisette ultimately decided to step down as head writer for the season as she was expecting her second child.[6] She remained on the series as a regular writer, closely monitoring episodes involving Replikas and she returned full-time to co-write the final episodes. Bruno Regeste was selected to replace her. Along with the change in head writer, several of the series' long-time writers did not return for Season 4; including Françoise Charpiat and Laurent Turner (who stayed for the first episode, but left afterward). As a result most of the season's writers were newcomers.

The budget for Season 4 was further reduced during production, which resulted in several planned Replikas being cut.[6][4] One of which was for a Mountain Replika, which already had background art created for it. As Mouscadet recalled: "[...] in season 4, we should have had a lot more Replikas, for which we had other sceneries in reserve. There was a Mountain Replika, at the vicinity of a dam, which would have looked quite good. But when you are doing a scenery model like this, it is a lot of work, because you have to also draw the interiors... [...] So for a realistic depiction, you need both shot and reverse shot, so it’s already two sceneries, and so on… So things can pile up quite a bit…".

While the season was in production, the producers relayed to the writers that it would be the last one.[4] According to Mouscadet, a regime change had occurred at France Télévisions (the owner of France 3), and the channel's new leadership were not interested in renewing their contract for the show.[7] As a result they decided to write an ending for the series. Decroisette was happy about the opportunity, noting both the rarity of serialized storylines in Western television and how uncertainty on whether a series will be renewed often lead writers to create cliffhangers that go unresolved.

When it came time to write the final episodes, Decroisette co-wrote them with Regeste. Going into them, she felt: "I didn’t want a final battle. I thought it was nice to have a “technological” ending [...] Not to mention that Jérémie is central in the series. We wanted him and his abilities to be decisive in the end. [...] we didn’t have any instruction against a final battle or budgetary constraints. In our opinion, the two enemies that fight each other are really Jérémie (who is in some way the equivalent of Franz Hopper, as they have the same abilities) and Xana. This was the conflict we had to solve."[4] One of the compromises with the budget for the season was that the producers mandated one episode primarily consist of recycled animation. The team decided to save this until the series finale and incorporate it into the plot, with Decroisette saying: "this is an episode where [the heroes] remember, really. We decided to do this thoroughly: they remember and they realize that it’s over." Higher-ups were mixed on this decision, and Decroisette said they "had to fight for [the] episode", explaining "it was a contemplative episode where almost nothing happened. It was also quite nostalgic and rather self-centered, with a somewhat deep subject."

Scripting for the season began in June 2006 and ended in March 2007.[8][9]


  • Chronologically this season is set during the 2003-2004 school year.[10]
  • Yumi, Aelita, Odd and Ulrich don new attire on Lyoko, which debuts in the season's second episode Double Take. Almost every character gets new attire on Earth as well, which first appears in Maiden Voyage and is seen in every episode after (except for The Lake).
  • When discussing the cut Replikas of the season, Decroisette clarified the Volcano Replika from Quest for Infinity was not one of them, and that it was created specifically for the game.[6]
  • Starting about halfway through the season, dialogue is occasionally sped up digitally in order for it to fit the character's mouth movements, causing it to sound distorted. Although this is commonly assumed to be exclusive to the English dub, the French version speeds up lines as well.[11]


(For production numbers)

  1. 1.0 1.1 "2006 - 2007: The series climax (seasons 3 & 4)" -
  2. "Interview with Sophie Decroisette" - (2007)
  3. Reply from Sophie Decroisette to Saisons 3 et 4: Réactions à l'annonce officielle: "Hello everyone,
    I've come to add a few grams of explanation to your topic.
    There will be 45 episodes written, divided into two seasons: 3 & 4.
    - Season 3 will be 15 episodes long and will be a direct continuation of season 2 (with lots of new concepts all the same). We're currently writing the first episodes. These 15 episodes will include the prequel (a double episode recounting the meeting of the heroes).
    - Season 4 will be 30 episodes long and will be full of conceptual and visual innovations (I won't tell you more). I'm still thinking about the concept.
    And there you have it!
    Kisses to all,
    Sophie". November 10, 2005.
  4. 4.0 4.1 4.2 4.3 "Interview - Sophie Decroisette, partie 2". Ces Dessins Animés-Là qui méritent qu'on s'en souvienne. March 11, 2014.
  5. "Interview - Sophie Decroisette et Jérôme Mouscadet, partie 3". Ces Dessins Animés-Là qui méritent qu'on s'en souvienne. March 18, 2014.
  6. 6.0 6.1 6.2 "Interview with Sophie Decroisette" - (2016)
  7. EXCLUSIVE interview with the creators of Code Lyoko... a potential SEQUEL ? ft. @Oliarius (2:09:07) - YouTube
  8. "From scripts to episodes S4 - Part 1 -
  9. "From scripts to episodes S4 - Part 2 -
  10. "Timeline > The official chronology and clues" -
  11. "French vs English" -