Name : Jeremie/Jeremy Belpois

Everyone should keep in mind that officially the second spelling is the right one. In the first season of Code Lyoko when aired in France, “Jérémie” was written in the French way. But because English-speaking people do not pronounce “ie” and accents, “Jérémie” was later made to change into “Jeremy”.
On the French version of this website, we kept the French spelling in all pages because we prefer the spelling from the first season. But as this part of the website is for foreign people, you will find “Jeremy” spelled with a -y at the end and without accents.

Nicknames: 
Einstein
Four eyes

Height : 1.47m / 4.82 ft

Weight : 31 kg / 68,34 lbs

Age at the start of the series : 12

Other :
Jeremy hates sports. For example, he prefers skipping the swimming class to spend more time working on materialization in the first season. In the second one, we seldom see him wearing sports clothes. However, he is very good at cross-country races because he always has to run when Xana launches an attack.

To see what Jeremy Belpois' life is like, here is an extract of his interview by Milly and Tamiya :

Milly: “For breakfast, do you like juice or milk?”
Jeremy: “Hot chocolate.”
Milly: “Eggs or toast?”
Jeremy: “Cereal.”
Milly: “Butter or jam?”
Jeremy: “Maple syrup.”

Jeremy is in the same class as Odd and Ulrich (and from episode 26 “False Start” on, as Aelita). Although perceived by his teachers as a young prodigy, he is fiercely envied by Herb who wants the top place. Jeremy is the brightest of his class with 19.87 /20 (A+) but Aelita is close behind him with an average grade of 18,5/20 (A+ too) and then comes Herb. However, his cleverness is not always an advantage. In episode 11 “Plagued”, the school psychologist who has kept an eye on Jeremy for a while decides to have him take some tests to check if this young Einstein is really a gifted child or not and if he is, to send him to another school...
The teachers are obviously praising him a lot for his results.

Jeremy is leaving at school like Odd, Ulrich and Aelita. Unlike his two friends he does not have any roommate, which is for the best as he spends all his time working on Lyoko, materialization, anti-virus software, and research aiming to allow a direct input into the network.

Besides, this research takes so much time that his grades end up dropping. In episode 64 “Double Trouble” Jeremy even drops behind Herb.

Needless to say that the only dreadful subject for Jeremy is sports. Jim never lets go of the chance to remind him so by calling him “slug”, “legless slug”, “soft-shelled crab” or other slow animals.

Jeremy is a gifted child... and his parents are very proud of him ! We know very little about Jeremy's parents. Actually only his father – Michael Belpois – briefly appears in the series, and only twice (Episode 49 “Franz Hopper” & 82 “Distant Memory”).
Jeremy says about him that he “adore[s] [his] dad, but…he’s sure no genius!”. This would imply that he does not have a good relationship with his parents. Besides, he often spends his weekends and even his holidays at Kadic boarding school (Episode 3 “Holiday in the Fog”).

What you can notice about Jeremy's parents is their kindness and the endless attention they pay to their son. In episode 49 Jeremy's father immediately comes after his son gave him a call and is not offended that he has to go back as quickly as he came. In episode 82 the Belpois family invites Aelita to spend Christmas at their house although traditionally it is rather a family celebration.

In episode 11 “Plagued” when Jeremy almost changed schools, one of the psychologist main points to convince his parents was that if Jeremy went there he would be granted a considerable scholarship. This comment suggests that he has modest origins and that his parents won't easily disregard this asset. In spite of this we cannot jump into conclusions and say that Jeremy's parents are only interested by money, otherwise they would be poor parents ! Jeremy seems to be an only son but nothing ever allows us to check this fact.

However, in episode 88 “Cousins Once Removed” we discover that Jeremy has a cousin. Patrick Belpois – a cool and trendy young boy – comes to Kadic. Jeremy cannot stand him because of old quarrels that go back to their youth. He remembers all too well the summer camps when Patrick was popular whereas he was neglected. Nevertheless, faced with Patrick's goodwill, he ends up giving in and reconciling. But after all, his cousin is not staying at Kadic.

In several episodes Jeremy dazes us with a flow of observations about computers – gibberish that his friends do not seem to understand at all ! He is often interrupted by Odd who kindly gets him to understand that computer science is not their cup of tea, and thus, he need-not try to explain it to them. Some of his most famous replies are: “In English?”, or “can you give us the CliffNotes version?”. Yumi is the only one who can more or less understand his research... but unfortunately not enough to do things like virtualize him for example. Unlike his Lyoko-warrior friends Jeremy does not really have his own power. His only gift is his great knowledge in computer sciences and any related fields (like robotics in episode 20 “The Robots”), which can turn out very useful when you have to deal with a “super-psychopathic computer” !

Jeremy's capacities are in constant evolution and this aspect of the character is often forgotten by the fans. In the beginning Jeremy is clumsy, some of his attempts become failures. In episode 38 “Temptation”, he unsuccessfully tries to use Hopper's brainwave amplifier helmet that he found in the lab...

However, Jeremy has the most useful capacity: learning... and really fast. This side of his personality is crucial because it enables him to face the harsh reality imposed by XANA. Jeremy always has to react to the program's tricks and most of the time he finds how to counter attack.
From the discovery of the direct access codes to Carthage because XANA began to destroy the main sectors, to the recreation of Lyoko, and the Skidbladnir to explore the network, without forgetting the “Energizing” that can destroy the enemy's supercalculators... The genius is never helpless. The harsher the fight, the faster he innovates.

Moreover, it is thanks to Jeremy's Multi Agent Programs that XANA received the knock-out blow and was eradicated from the network.

In the whole series, Jeremy is the driving force. From the first episode on, we can see that Jeremy is the one in charge of the supercomputer in the lab. Thus, he is the machine-operator. Monitoring, computer manipulation, detection of the enemy's every moves, of any danger... Jeremy is crucial so that the operations run smoothly on Lyoko.

Other than his everyday tasks, Jeremy is also one of the keys to the progression of the plot. His success untie the knots in tricky situations and help in the advancement of the series: Aelita's materialization, looking for Aelita's anti-virus before discovering the existence of her missing link, the network conquest, etc...

So Jeremy is one of the most important members in the group. He makes void the expression “No man is indispensable”. If they were able to recruit a new Lyoko-warrior thanks to William, it is almost certain that they would not have been able to find another Jeremy. It is probably why he is one of XANA's favourite preys.

Once Aelita has materialized, Jeremy has a potential substitute for the operator position. Nonetheless, Aelita is required on Lyoko and is not as skilled as Jeremy. Aware of the mess that him going missing would drag his friends into, in episode 72 “Crash Course” Jeremy tries – with uncertain results – to train his team mates to the hard tasks he usually carries out. Yumi is the most capable as a replacement, like in episode 76 “The Lake”. Would her Japanese roots be part of the explanation here?

For everyone Jeremy – and his nickname reveals this all too well – is perceived as the young Einstein of the group, which means that the others cannot forgive him easily for his mistakes (Episode 49 “Franz Hopper” and 62 “Nobody in Particular”), and this is particularly unfair because as French people like to say “Only the one who stays idle won't make any mistake”...

Sentimentally less... let's say passionate than Ulrich, his platonic relationship with Aelita brings a second couple on TV for “snagless love” lovers.

Serious, respected, boring, and unattainable. These are the four words that would best describe Jeremy according to his classmates who willingly admit he is a young prodigy but consequently think of him as a workaholic or a bookworm – unattractive characteristic for the majority of the students. And over-simplistic image of Jeremy, deformed by their strong perception of his intelligence. Because in spite of this, would they only try to say a few words to him they would realise Jeremy is very approachable person. Yet, in all the episodes, except his friends, Sissi's group, William, Milly, Tamiya, and Heidi Klinger, no one from the school speaks to him... This is very little if we take into account that Kadic is a middle school and high school, meaning there is quite a lot of students.

Jeremy is a gifted child but being more intelligent than average makes him no more different than the other boys. In the contrary, he is very humane and has the same feelings as other people but unlike some he manages to keep a lot to himself (except for one thing...). He spends a lot of time enclosed in his room or at the abandoned factory's lab. He is working, all right... but not on what other people think he is. His ultimate goal is to turn off the supercalculator without risking Aelita's life and this requires much effort. In season 1, he spends whole nights chatting with his virtual friend and working on her materialization. In season 2, he is not busy with materialization any more but with the discovery of the anti-virus and in season 3, he is carrying a research to send his friends on the network so that they can fight XANA. With this description, one could believe that in Jeremy's life nothing is more important than finding a way to annihilate XANA and that for this purpose he is neglecting everything including his friends... but nothing is more wrong than that. He is on the move as soon as he knows one of his friends is in danger, transferring on Lyoko without a second thought in episode 24 “Ghost Channel” to save them from XANA, openly confronting him so as not to lose them. For Jeremy, life would be meaningless without Aelita, Yumi, Odd and Ulrich. He proves this to us in episode 24 “Ghost Channel” when he gets worried sick over their disappearance.

Jeremy, however, tends to disregard all things unrelated to Lyoko. From time to time, because of this unmeant indifference he even ends up hurting Aelita's feeling, like when he misses the Subdigital's concert in which Aelita is playing the first part (episode 89 “Music to Soothe the Savage Beast”).

His biggest flaw is his impatience, which is shown several times when he tries to materialize Aelita (episode 13 “Just in Time” and 6 “Cruel Dilemma”). His friends help him put a damper on his enthusiasm, getting him to keep his head cool and proving him conclusively that he just needs to wait a little more.

Aelita, a virtual creature, a dream creature for Jeremy who fell in love at first sight when they met at the factory. An unattainable creature, to the greatest dismay of the teenager who got into his head that he would help her materialize on the Earth.

This obsession that some would think of totally crazy will support Jeremy and his friends in this exceptional adventure, and will open the doors to a very special relationship with Aelita, young innocent, pure girl who knows nothing about the Human world. Jeremy spends most of his time with her in his bedroom. He is sitting on his chair in front of his computer contemplating Aelita on his screen, both so close and so far away from her, answering Aelita's questions about the Earth or helping her to find the key to her materialization.

Always ready to lift her friend's spirits when he thinks he is too useless to find the key to materialization, she helps him and support him as much as possible. From the start of their relationship to the first day she spent on the Earth including the long period she lived as a program, Aelita and him have only fought three times. In episode 19 “Frontier” Jeremy gets angry and makes up with Aelita after Yumi unsuccessfully tried to virtualize him the day after. In “XANA's Kiss” (episode 43) when the lovers come upon each other kissing someone else, but this is actually a trick from XANA to sow discord in the group – besides, in this episode you can see Aelita and Jeremy kiss for the first time. And in “Aelita” (episode 57) because Jeremy cannot understand why Aelita wants to find her father so much, the genius being convinced that he was eradicated from the virtual world.
Except for this three arguments, their relationship goes particularly well, Jeremy spending almost all his time with her while she discovers the world thanks to him.

After his friend's materialization in episode 25 “Code: Earth” some minor problems appear because of Jeremy's jealousy or sulking. One of the most serious case is in episode 32 “Saint Valentine's Day” when he holds Odd responsible for giving a necklace to Aelita.
Jeremy's personality also brings a few frictions like in episodes 33 “Final Mix” and 89 “Music to Soothe the Savage Beast” when he neglects Aelita's new passion for mixing.
In season 3 Jeremy does not pay much attention to his young friend. Some fans find this regrettable but with Lyoko's imminent destruction, rather than wooing he has other things to do.

In truth, there are two things to understand:
First, Aelita and Jeremy are in love with each other but their respective personalities being what they are – shy – they do not dare admitting it, preferring to stay hidden, using knowing tricks like the codename “Big Fat Cheesehead” (episode 72). Knowing their feelings for each other, they do not feel the need to spend their time talking about them.
Secondly, the scenes when they spend time together do not always appear in the series ! How many nights have they spent working together?

Maybe one day we could hear one of our lovers softly uttering “I love you”...

Jeremy is the one who switched on the supercalculator once again. He had discovered it by chance while looking for components to build his little robots in the neighbouring abandoned factory's hidden laboratory.
On October 9 2003 he switched on the supercalculator and discovered at the same time by typing some things on the supercomputer's keyboard a virtual young girl just waking up thanks to the start of the machine. Curious at first, he wondered if it was a kind of game until the young girl asked him who he was and where she was. Then everything changed.
A bit later, after attending his classes, Jeremy went back to the factory and gave a name to the A.I: Maya (that we are going to call Aelita at once as it is her real name). They discovered together that the virtual environment where Aelita lived was called Lyoko but that she was not alone in this world...

The day after, wanting to buy a drink from the vending machine Jeremy found himself electrocuted right in front of his classmates' – Ulrich Stern and Odd Della Robia – eyes. Ulrich brought him to the infirmary while behind their backs, a strange symbol appeared for a few seconds and disappeared from the vending machine's keys.

In the evening, whereas the young genius was working on his computer in his room, the screen turned blurry and the same strange symbol appeared while a little robot just beside Jeremy, on his desk, started moving on its own and attacking him, quickly joined by another one. The boy stepped back while both robots began sending him electric discharges.
The door was kicked opened by Ulrich Stern who was in the corridor and had heard Jeremy scream. The teenager helped the young genius to break free from the robots' grip and got rid of one of them at the expense of being shot a few time himself by electricity.
Ulrich asked to know about everything. Jeremy refused but the boy is stubborn and Jeremy surrendered. He was beginning to doubt his own ability to deal with this alone and thus chose to reveal his secret to his friend. He brought him to the factory where Ulrich met Aelita. Sceptical at first, he was then slowly convinced by Jeremy and after hearing his crazy blabbering about virtualization, he agreed to try it... using Kiwi – the dog of Odd Della Robia, a new student in the school who shares Ulrich's room.

When Ulrich came back to the lab after having left Kiwi in one of the scanners, Jeremy started to virtualize it before realizing the dog was not in the chamber.... Odd Della Robbia was ! Though he was worried he just watched the process, not knowing how to stop it. The problem was solved since Odd and Ulrich – virtualized soon after Odd – were devirtualized by Blocks.
In the meanwhile, Jeremy was attacked by electric cables trying to electrocute him but he was saved by Odd and Ulrich while Sissi just stood in the goods lift, watching him and screaming but doing nothing.
The day after, Jeremy announced to the others that he found a way to materialize Aelita – this being his new obsession. According to him, the red Tower that Ulrich and Odd had seen the day before would be they key to her materialization on Earth. Their mission, once on Lyoko, would be to escort Aelita to the red Tower. Because of Jeremy's insistence they all swore to keep the secret.
During the day, Odd and Jeremy heard that Sissi was electrocuted by a big electricity ball. Both dashed to the factory, joined by Ulrich and a young Japanese girl called Yumi that he met at Jim's – the monitor's – martial arts class and who was there when Ulrich was almost electrocuted himself by the same electricity ball that had hit Sissi.
Once at the factory, Jeremy virtualized Yumi, Odd and Ulrich to meet with Aelita and escort her to the red Tower.
When she got to the Tower she did not materialize, to the great dismay of Jeremy who was forced by the Principal – that Sissi brought – to stop everything and then the genius launched his first return to the past... which erased his memory like the others' apart from Odd, Ulrich and Yumi because they were on Lyoko so the supercalculator had recorded theirs. They had to explain everything to Jeremy.
The following day, after having spent the night looking for data about Lyoko with Aelita's help, Jeremy informed his friends that he had found the name of the thing who had attacked them: XANA. The four of them swore to fight XANA and Jeremy promised Aelita he would materialize her as soon as possible.
The beginning of a long quest.
It took more than one year to Jeremy to find the key to materialization. He spent days and nights working on it while still attending his classes and fighting XANA when the latter launched an attack. He never went on Lyoko and that was Odd's favourite teasing subject but in “Ghost Channel” he went too far saying Jeremy was not a real hero because of this. Though Jeremy proved him mistaken by going to save his friends in the virtual bubble that XANA created in that same episode. He fought XANA – who had copied his looks – thus showing that XANA's theory during their confrontation about him being too afraid to go inside the scanners was wrong. Odd answered that on the contrary he would do it if his friends were in danger.
Jeremy finally finds the key to materialization ! Sheer moment of happiness when at last Aelita appeared in front of them in one of the scanner in flesh and bone, but this happiness quickly turned into bitterness when after trying to shut down the supercalculator Aelita fainted and he discovered that Xana had implanted a virus inside her to link the both of them. The materialization succeeded but his hope to turn off XANA went up in smoke. A new research began: looking for the anti-virus for Aelita.
Helped this time by his materialized friend who began attending classes with the three boys – Yumi being one year older – he also spent a lot of time on this research. He still attended his classes while fighting XANA and never went on Lyoko...
This will cause him trouble later on because in episode 31 “Mister Pück” XANA possessed his body – capacity that he obtained just before in episode 30 “A Great Day” thanks to the numerous return to the past that the virus had launched to increase his power. He possessed him to hand over Aelita to the scyphozoa, a monster sent by XANA who for an unknown reason wanted to steal the girl's memory and was ready to “xanafy”anybody (take possession of his/her body) to reach his goal. XANA killed two birds with one stone on this occasion by destroying the encoded diary of the mysterious Franz Hopper – an old teacher from Kadic also owner of the Hermitage, the place where Aelita had her strange visions that seemed inexplicably related to Lyoko. But both were failures because Yumi, Odd and Ulrich managed to take Aelita from the scyphozoa and Jeremy who had planned this had copied all the CDs in an extremely well protected part of the supercalculator's memory, that only him would be able to access. To protect himself against the ghosts, Jeremy went to Lyoko a third time although we were not able to see that.
Unfortunately, to find the antivirus, Jeremy was ready to do anything, even harm his body with brainwave amplifier helmet to increase his cognitive skills. He was trapped by XANA who had him make several returns to the past to use the helmet, increasing at the same time XANA's power.
Jeremy worked on two projects simultaneously: the antivirus and Franz Hopper's diary. When Hopper appeared, Jeremy was charmed and trusted at once this mysterious man like the others... but the young prodigy quickly changed his mind when Franz Hopper began blaming him for using the scanners and found that Yumi's cells were degenerating.... This split up the group ! Odd, Ulrich and Yumi together against Aelita supporting the disheartened Jeremy.
But everything quickly came back together when Franz Hopper sent Yumi, Odd and Ulrich on Lyoko, giving them new weapons before making them disappear! Jeremy knew what was going to happen and saved Ulrich at the last minute. Actually it was not Franz Hopper but a ghost sent by XANA to mess with the group that made peace almost at once as the problem was solved.
This break was short though. Sissi suddenly began behaving oddly, as if she wanted to say something to the heroes but she could not speak with intelligible words and just babbled nonsense. In the evening she woke Jeremy up to write an obscure message... it was not written in English but with numbers and weird codes.
When Jeremy managed to decipher the codes, he found this message: the entity that had taken control of Sissi was no one else than Franz Hopper trapped in the virtual world who was trying to help them.
Soon after, Jeremy announced that thanks to the data he had found on the fifth territory he was able to read Franz Hopper's diary. After some hardships, Jeremy revealed to his friends that Franz Hopper had a daughter that he virtualized with him when going on Lyoko... and that this girl was Aelita !
So everything quickly began to make sense. Aelita did not had a virus, it was a fragment of her memory that remained in the fifth territory. That was why the scyphozoa kept attacking her. She had Lyoko's key in her memory. If XANA could obtain them he would be free... Aelita managed to get back the missing fragment but XANA took advantage of the situation and after erasing our heroes from the virtual world, he managed to steal Aelita's memory using the scyphozoa. So now XANA had Lyoko's keys and was free !
Thanks to Franz Hopper's intervention Aelita was saved though she had died from having her memory taken from her. Moreover, she was not linked to Lyoko any more. She was now a human being in her own right !
But knowing that XANA was free, the happiness brought by this victory was not complete. From nowon, Jeremy's new mission was not to find an antivirus or even the key to materialization but how to send his friends on the net because it was XANA's new domicile. Because of Aelita's tenacity Jeremy began a research about where Franz Hopper could be as he had discovered a fragment of the scientist's DNA sequence code. The genius had now two goals. Or rather three as XANA had decided to destroy Lyoko. But if Lyoko was destroyed our heroes could not do anything anymore when attacked and the real world would probably be destroyed too.
However, XANA had more and more power and sometimes they barely managed to contain his attacks. XANA had found various ways to destroy the virtual world but the one that succeeded was xanatifying Aelita so that she could destroy the main territories one by one. gagnait de plus en plus en puissance et à bien des reprises, ils eurent du mal à contenir les attaques. Slowly but without a fail the virtual world began to decline before disappearing completely when William – new member among the Lyoko-warriors – controlled by XANA destroyed Lyoko's heart, crushing at the same time Aelita's hope that she could at last see her father again...
The fight against XANA seemed like it was coming to an end and the heroes were disheartened. They had failed their mission and now the world could be destroyed at any time... Then, suddenly Jeremy's computer made a beeping noise. He had received an encoded message from... Franz Hopper !
Maybe the end had not come yet...


Not allowing themselves to rest, Jeremy and Aelita worked for a whole week on Hopper's message. It contained data and directions to rebuild Lyoko ! The project was a success. The heroes launched the programme and the virtual world appeared once again, but only the fifth territory. The others territories were created soon after.

Jeremy and his friends welcomed a xanatified William... and nothing implied that this was going to change. Then comed a new problem. How were they going to justify William's absence at school. Jeremy used his speech synthesizer to save time, pretending to be William's parents. Then he activated a tower on Lyoko on which he had a strong grip. From this tower, he creates a polymorphique clone looking like William to replace him at school.

This “normal stuff” being taken care of (after all, recreate a virtual world is a peace of cake for everyone), Jeremy could concentrate his efforts on his never-ending mission: fight XANA. But things had changed. XANA was not trying to destroy Lyoko and the Supercalculator at any cost, just one or twice for fun [Episode 74 “I'd Rather Not Talk About It” & 81 “A Lack of Goodwill”]. Moreover, Hopper had contacted them and was still on the Network. This is also where William ran away when defeated on Lyoko, hiding under the appearance of dark smoke.
This was leading to only one conclusion: if XANA, William and Hopper were on the Network, then they had to go there to solve everything.

Jeremy then studied what was the network. 
He discovered that Lyoko was just a small bubble in the vastness of the numerical Ocean, and the numerical Sea around each territory was just an extension of the Network entering Lyoko. This numerical water represented the flow of data from the Internet Worldwide !
Getting deeper into the subject, Jeremy realized that Lyoko had a direct access to the Network, like an exit airlock... Sadly, the virtual body of the heroes could not get into the Numerical Sea or they would be crushed and dispersed in the gigantic flow.

Jeremy, helped by Aelita found the solution. A vessel that could go through the Network and carry the heroes. This submarine was called the Skidbladnir (Episode 70 “Skidbladnir”).
Jeremy programmed it as Aelita modified the configuration of the fifth territory and created a garage to put it away. XANA tried to destroy it twice (Episode 70 and 76 “The Lake”).

Then came the first travel.
Jeremy, as usual stayed behind as their operator while Aelita piloted the Skidbladnir in the Network. The numerical Magellans hoped they would find some tracks of William or Franz Hopper to bring them back to the scanners... but they found something else.

During the trip they discovered an island and transmitted the information to Jeremy who identified it. It was a Replika ! A copy of Lyoko. A small virtual world with only one territory.
The news were alarming but as always, the young prodigy accepted the challenge and analysed it. XANA after escaping to the Network had a direct access to the World Network. However, he still needed energy from the Towers to attack. That was why he had invided the Supercalculators of the World. Even if Franz Hopper's one was the most powerful ever, XANA had found through the World's Supercalculators a way to create this kind of small replica of Lyoko. Thanks to them, he had Towers to give him energy.

Jeremy then calculated that if XANA had no place where he could stay he would be destroyed. Without the Replika, XANA was no more. And to destroy the Replika... they had to destroy the Supercalculator that created it.
Jeremy innovated once again a new method called “Translation”. By entering a Replika, the Skidbladnir could dock on one of the towers. From then, Jeremy could send the heroes as Ghosts near the Supercalculator generating the Replika.
Once they were there, they could destroy the Supercalculators with their powers.

Jeremy guided the heroes in the most dangerous missions through the Network, the Replikas and the bases sheltering the Supercalculators... as well as XANA's traps.
He always accomplished his operator's tasks brillantly, analysing the structure of the Supercalculators he wanted to destroy, unlocking the doors that had an entry code etc...

In the meantime, daily life was not so easy... XANA wanted to throw Aelita in the Numerical Sea to have Hopper appear as he was the only one able to save people from falling into the Numerical Sea.
Jeremy was always a good target as he was the group operator. So he tried to transmit some of his knowledge to his team-mates (Episode 72 “Crash Course”). He also had sometimes to make up for Odd's blunder when he tried to virtualize Kiwi (Episode 80 “Dog Day Afternoon”), or to fight a xanafied Sissi with his cousin who came to visit him (Episode 88 “Cousins Once Removed”). Jeremy even had to train his body with GI-Jim in Episode 74 “I'd Rather Not Talk About It”.

Fortunately enough, some good things also happened, like spending heartwarming Christmas holidays with his family and Aelita.

Then came the (long awaited) time when XANA made a mistake. While the heroes were translating somewhere, XANA translated William to block them by activating one of the Replika's Tower. Once in the Tower Aelita took the missing information they needed. Very quickly Jeremy elaborated a programme and there you go ! William successfully devirtualized and appeared out of the scanners (Episode 92 “Cold Sweat” and 93 “Down to Earth”).

It was high time because XANA had showed up with a new weapon: the Kolossus. An ultra-powerful monster able to smash the Skid very easily... the destruction of the Replika had thus become impossible... And anyway, Jeremy had discovered that there were too many of them.

Feeling stronger now that William was back, Jeremy began working on a new project: destroying XANA thanks to a multi-agent system or “fight fire with fire”.

As Jeremy was concentrating on developing this something unexpected happened: Hopper sent a message. He asked the heroes to go to Lyoko, transmitting the missing data to Jeremy so that he could finish the programme and end the fight with XANA... who attacked at once !
Jeremy hurried to get the data and sent Aelita on the fifth territory to start the programme...

To top it all, they were short on energy so it did not work.
Hopper then decided to sacrifice himself. Using his own energy to Aelita's utter despair, he allowed Jeremy to start the programme but got killed by the Mantas before Jeremy could materialize him.

The programme spread in the Network under the shape of small white agents and destroyed XANA and his Replikas, ending the war. Jeremy welcomed the heartbroken Aelita in the scanner room.

It was then time to turn off the Supercalculator and to end everyone's lives as super-heroes.
But Jeremy could not turn off the machine that he had turned on months ago. And even though Yumi blamed him, his other friends supported him. It was difficult to put an end to such an exciting life.

Confiding in Aelita, he admitted that he feared going back to his old boring geek self and to be left alone like before. However Aelita managed to confort him.

After the Lyoko-Warriors had all come back mentally prepared, Jeremy turned off the machine and ended this unforgettable period of his life.