The World Seed (世界の種子, Sekai no Shushi?) is the twenty-fifth and the final episode of the Sword Art Online anime adaptation, as well as the eleventh and final episode in the Fairy Dance Arc. It aired on December 22, 2012.
Kirigaya Kazuto continued riding his bicycle to the hospital, but fearing for Yuuki Asuna's safety, he peddled faster and eventually arrived at the parking lot. As he ran towards the entrance, someone appeared and lacerated Kazuto's right arm. When he realized that he had been cut and saw blood dripping, he turned around to identify his attacker, Sugou Nobuyuki (Oberon). Nobuyuki was angered that Kazuto not only thwarted his plans, but also caused him immense pain, since if the Pain Absorber level was set to level 3 or below in ALfheim Online (ALO), the pain also affected the person's real life body and Kirito had set it to level 0 during their duel before slicing Oberon into pieces. Kazuto advised Nobuyuki to turn himself in, but the latter refused, stating that other companies would accept and shelter him due to wanting his work. He then decided to kill Kazuto to take his revenge on him.
Kazuto fell on the pavement as an attempt to dodge Nobuyuki's attack, but was then repeatedly kicked by him. Finally deciding to finish him off, he tried to stab Kazuto, but missed, as his right eye was still blurry from Kirito's attack. Nobuyuki then tried stabbing him again, but this time Kazuto grabbed his arm and reversed the situation. Kazuto pushed Nobuyuki off him, took the knife, smashed Nobuyuki's head against a car and put the knife to his throat. Contemplating everything he had done to him and Asuna, Kazuto was about to kill him for revenge, but ended up sparing him and left the fainted Nobuyuki in the parking lot for the police to arrest him.
Arriving at Asuna's room, Kazuto paused for a moment before a voice encouraged him to continue, and he moved the curtain to find Asuna waiting for him. He came up to her and told her that everything was finished, even the "true final battle" that occurred moments ago. They then hugged, kissed and revealed their true names to each other as if they had only just met and fell in love. Kazuto looked at the window and saw their Sword Art Online (SAO) avatars, who held their hands and left together.
Months later, on May 16, 2025, Kazuto was at his new school. As one of his classes was now over and it was time for a lunch break, he walked to the park outside the school, where Asuna was waiting for him. She greeted him as Kirito but he reminded her that it was bad manners to call another person by the names they used in games, and teased her for using her real name in a game, but they laughed when they remembered that the school was specially formed for the survivors of the Sword Art Online incident who were still students, so everybody had to have guessed their identities by now, due to their in-game avatars being replicas of their real life bodies. Kazuto then asked Asuna about her rehabilitation, and she replied that she no longer needed a cane, but was advised not to run. As he held her hand, Asuna informed Kazuto that the park was visible from the cafeteria, and, in response, he let go of her hand and apologized. She teased him that it would cost him lunch, though Asuna had a basket of food that she served him in SAO.
As they were having lunch, Asuna informed Kazuto that her father, Yuuki Shouzou, had resigned as CEO of RECT. Kazuto then reminisced how on that snowy day, Nobuyuki was arrested in the parking lot and was then interrogated, trying to frame Kayaba Akihiko for the experiments, but once one of the employees agreed to testify, he confessed. The 300 players who had not escaped from SAO were freed and did not remember anything that happened during their experimentation and fortunately did not suffer any neurological problems, thus they could return back to society. However, because of Nobuyuki's inhuman experiments, the VRMMO game industry's reputation was even more damaged than it already had been due to the SAO incident. RECT Progress Inc. was disbanded, and even the main RECT branch suffered a huge loss. ALO was shut down, along with Kazuto not expecting five or six other VRMMO games to survive for long either.
Asuna then asked what happened to the commander of the Knights of the Blood, Heathcliff (Kayaba Akihiko). Kazuto told her that he had died, and the authorities suspected that he had committed suicide. Kazuto then explained that when SAO collapsed, Akihiko performed a high-output scan on himself, which was to copy his consciousness onto the Internet, which had a one in a thousand chance of succeeding. Kazuto thought about Akihiko because of meeting him in ALO and also thinking about the seed program the latter had given him.
As Kazuto became lost in thought about Akihiko, Asuna reminded him of the meeting with the others, teasing him on his habitual inattentiveness, before affectionately leaning against him. Meanwhile, in the cafeteria, Shinozaki Rika (Lisbeth) angrily watched them, seething over her juice. Ayano Keiko (Silica) told her to stop slurping so loudly and watching them. When Rika complained about Kazuto and Asuna being so intimate at school, Keiko told Rika that it was her fault for agreeing to let Kazuto and Asuna enjoy themselves for one month without taking any action herself, something Rika regretted. Shortly afterward, Rika asked Keiko if she was going to the meeting later, to which she replied affirmatively.
In the afternoon, Kazuto and Asuna were walking on the street holding hands, while Kirigaya Suguha was following them quietly. Kazuto then turned around to ask her if she had met Andrew Gilbert Mills (Agil). She answered that she had hunted with him twice in ALO, so Kazuto warned her that he was equally tall in real life. When they arrived at the Dicey Cafe, everyone was already there. Kazuto asked for confirmation whether they were late, and Rika teased him that the stars always arrive last because they told them to come at a time a bit later than everyone else gathered. After leading him in, everybody congratulated Kirito for clearing SAO and freeing them from the game, much to his surprise.
Kazuto then went up to the bar and asked for bourbon, but Andrew instead handed oolong tea. Tsuboi Ryoutarou (Klein) walked up to them and made the same request, stating he could not pull overtime on work without alcohol, plus everyone was enjoying themselves. When Thinker also joined them, Kazuto and Ryoutarou congratulated him for marrying Yulier in real life, before discussing Thinker's gaming information site, «MMO Today».
Kazuto then asked Andrew about the World Seed and how the VRMMOs were developing, and Andrew told them that it was going well, with 50 mirror servers, 100,000 downloads and 300 major servers that were running it. Kazuto then narrated that he gave Akihiko's World Seed to Andrew to analyze it and they discovered that it was actually a program that ran a VRMMO creation and management package, called «The Seed», a modified basic version of the Cardinal System program. In essence, anyone that had access to a good enough server could download The Seed and create their own virtual reality world. Kazuto requested Andrew to upload it to public servers for anyone to download for free, thus the VRMMO industry was revived. ALO's data was transferred to another company, which was created after the ALO incident by former players of the game, while other companies and even people began to run their own server of their own game, and those began to be compatible with the others, achieving the goal of the same avatar being usable in different games. Kazuto then asked if they were all still going to the afterparty, and Andrew said that they would gather at Yggdrasil City as planned. Meanwhile, Suguha was sitting alone, feeling left out from the SAO survivors.
In ALO, Leafa was flying alone above the Cait Sith territory and tried to reach the moon, but was stopped by the Altitude Warning sign. While falling, she recalled the recent events of the party and in the clouds she was caught by Kirito, who had come to get her since they were about to meet with the others soon at Yggdrasil City. She asked him why had he not returned to his SAO avatar like the others, but Kirito replied that the job of his SAO avatar was completed. She then taught him of a new mechanic in the game, dancing, and opened a bottle which played music for them, all just to lighten up the mood, since she was sad that she would never be able to catch up to everyone else. Kirito did not believe her as he believed that she could go wherever she wanted, so he grabbed Leafa and started flying towards Yggdrasil City, but did not manage to reach it on time. He stopped midway near the World Tree and showed her a giant floating castle that came into view: New Aincrad.
Surprised, Leafa asked why was it in ALO and Kirito explained that this time he was going to finish it to the end. He then told her that his stats had been reset and asked her if she would help him to which she gracefully agreed. At Klein's mild rebuke for their tardiness from behind them, Kirito and Leafa turned to see him, Agil, Lisbeth, Silica, and Pina, along with Thinker, Yulier, Sasha, Sakuya, Alicia Rue, Recon, Eugene, and other Sylph, Cait Sith, and Salamander players, heading to the New Aincrad. Asuna, now an Undine character, stopped and called for Kirito and Leafa, as well as Yui appearing and sitting on the shoulder of her "papa". Kirito muttered something before starting to fly, surprising Asuna and Leafa, but then just said "Okay! Lets go!" as everyone flew to Aincrad.
- Real World: Torokazawa Hospital, School, Dicey Cafe
- ALfheim Online: the skies near the World Tree; New Aincrad
- Kazuto did not tell the receptionists what happened in the anime, while in the novel he told them and grabbed a guest card in the process before heading off to see Asuna.
- It was not mentioned known orange players put under counseling and observation after the SAO incident.
- The mention of Kazuto's conversation with Koujiro Rinko was omitted.
- Caynz and Yolko were not explicitly mentioned to be among the party members in the light novel.