On November 1st, in the 1st Floor main settlement, the «Town of Beginnings»; Kirito and his family were having their breakfast at the guestroom of the church, where Sasha and the children players were residing in. Kirito and Asuna were amazed at how many children players there were in the church. After a night's sleep, Yui had recovered from her panic attack earlier. Sasha explained to Kirito and Asuna that ever since the announcement of the death game, she felt it was her duty to look after the children trapped in the game and thus she went on daily walks in the town in search of children players, but informed them that she had never seen Yui. Just then, they received a visit from Yulier, the vice commander of «The Army». Instead of complaining about them fighting her guild members, Yulier thanked Kirito and Asuna for punishing her fellow «Army» members who were causing trouble. She then told them that she came to ask for their assistance.
Yulier explained that the «The Army» became more corrupt and irresponsible thanks to the efforts of its former sub-leader: Kibaou, who was trying to overtake leadership from the nominal guild leader Thinker. The guild became corrupt when Kibaou came into power and enacted upon collecting taxes from people in the Town of Beginnings, and people were led to believe that he no longer cared about clearing the death game. As an attempt to dissuade this, Kibaou sent Kobatz and his men to challenge the Floor Boss of the 74th Floor by themselves, which resulted the deaths of Kobatz and two of his subordinates, thus the guild planned to exile Kibaou for this reckless action. Desperate, Kibaou lured Thinker into a high-level dungeon without any equipment or crystals, under the guise of apologizing to him for the incident. Once Yulier heard about two high-level players that had come to the 1st Floor, she went to find them. Kirito and Asuna had doubts about Yulier's story, as it could have been a trap. However, after Yui stated that she somehow knew that Yulier was telling the truth, Kirito chose to believe in her story, instead of later regretting not helping her, and thus they agreed to help. Kirito and Asuna then told Yui to stay with Sasha for safety, but Yui insisted to come with them. Having no other option, Kirito, Asuna and Yulier took her along.
As they entered the dungeon, Asuna and Kirito commented on how they had never realized such a large dungeon existed underneath the Town of Beginnings, and how it was not present in the Sword Art Online closed beta service. Yulier explained to the group that the dungeon was speculated to have been unlocked as the Clearers made progress on the higher floors, and stated that Kibaou wanted to have this area for The Army's personal benefit; however the monsters were too strong for him, so he could not use it as much. During their progress in the dungeon, Kirito enjoyed himself by defeating a group of Scavenger Toads they had come across, with Yui cheering on. Yulier felt apologetic about compelling Kirito to handle all the monsters, though Asuna assured her that Kirito did not mind. Yulier then checked her map and discovered that Thinker remained in one spot, most likely a safe zone. After the battle, Kirito told the others that he had collected items from the monsters, most of which were Scavenger Toad Meat which he hoped Asuna would cook later. Instead, she disposed of them all in shocked disgust, to Kirito's dismay and despite his protests; the scene prompted Yulier to smile, an action that Yui noticed and expressed joy about, which pleased Asuna in turn.
The group finally arrived in a corridor with the safe area in sight. At this moment, Kirito used his Searching skill to confirm that Thinker was trapped in there. Overjoyed with the news, Yulier began running towards him, but Thinker yelled to her to not proceed, warning that the corridor was dangerous. Immediately afterward, Kirito detected an enemy named «The Fatal Scythe» hiding in the shadows, and rushed to Yulier as Asuna vainly called to her to stop. As The Fatal Scythe was about to land a blow from its weapon on Yulier, Kirito jumped right on time and pushed her out of harm's way. Asuna then asked Yulier and Yui to run to the safe area and teleport out, to which she agreed, though Yui was concerned. Kirito was unable to identify the boss and presumed that it was as strong as a boss on the 90th Floor or above. Although he also asked Asuna to go with Yulier and Thinker, she refused and stood by him. As the boss attacked, Kirito and Asuna blocked the assault, but were blown away from the hit, lost half of their hit points in the process, and were unable to return to their feet.
As the boss was about to deal the finishing blow on Kirito and Asuna, Yui left the safe area, just as Thinker and Yulier were teleporting away, and stepped in front of The Fatal Scythe. The monster then attempted to attack her, but just after she told the couple that they do not need to worry about her, The Fatal Scythe's attack was repelled by an «Immortal Object» shield, which left Kirito and Asuna in shock. Yui then levitated, changed to the clothes she originally had when Kirito and Asuna found her and generated the «Object Eraser» in the shape of a huge flaming sword which she used to remove the boss with a large flaming sphere. Yui then told Kirito and Asuna that she had recovered her memories.
Back in the safe area, Yui, finally pronouncing the names of her so-called parents correctly, explained that the Cardinal System, which regulated the entire SAO server, created an AI called the «Mental Health - Counseling Program Prototype 1», codename Yui, who was given the ability to emulate emotion to put players at ease with her. She explained that she was intended to take care of the player's mental health, but, for reasons she never understood, Cardinal prevented her from interacting with the players, effectively forcing her to monitor their emotions without a way to interfere. She only saw hate, rage and desperation in the players until she saw Asuna and Kirito, who were enjoying themselves despite being trapped in the death game, and decided to get as close to the two. Yui, crying in happiness, wondered how it was possible for a mere program to think like that until Kirito told her that she was no longer being controlled by the Cardinal System, and thus she could think whatever she wanted. After Kirito asked what Yui wanted, she replied that she wanted to stay with them forever, and the family shared a tearful hug. Although Kirito and Asuna assured Yui that she would be with them forever, Yui sadly explained that she used a GM Console, the large black cube in the safe zone, to delete The Fatal Scythe, resulting in the Cardinal System detecting her presence and, due to her disobeying its orders, the system now recognized her as a "foreign object" and was proceeding to remove her from the system. Yui thanked Kirito and Asuna and requested them to help other players in her stead and to continue smiling before she turned into particles of light that vanished into thin air.
As Asuna descended into hysterical weeping, Kirito, cursed the Cardinal System and Kayaba Akihiko, then took the keyboard of the GM console while Yui's credentials were still active and managed to save Yui's program by transforming it into an in-game object, «Yui's Heart», which Asuna then wore as a pendant, while Yui's data was stored into his NerveGear's local memory. On the way home, Kirito and Asuna talked about recreating Yui after they escape from SAO. Yui's particles then floated by and her voice wished her mother good luck.
- Teleport Crystal x 3
- Teleport Crystal - given by Yulier
- Aincrad Floor 1:
- Aincrad Floor 22
- Adapted from Volume 2, Morning Dew Girl
- The discussion Kirito, Asuna, and Sasha had on the changes and divisions of attitudes among The Army members, as well as requesting Heathcliff to mobilize the Clearers to put The Army in line, was omitted.
- In the novel, it was mentioned that Kibaou used a Corridor crystal to send Thinker into the dungeon. This was omitted in the anime.
- In the anime, it was not mentioned that The Army found a very large boss in the Hidden Dungeon, nor was it mentioned that they had teleported out of the dungeon in panic.
- In the novel, Asuna herself accessed the shared inventory with Kirito and deleted the Scavenger's meat from the inventory without taking it out, while in the anime, Kirito materialised all of the meat from the inventory and Asuna literally threw it away, the whole incident ending with Asuna stuffing one of the legs into Kirito's mouth.
- In the light novel, Kirito fought against crayfish-like monsters. The crayfish-like monsters were not seen in the anime.
- In the novel, when Thinker warned the group to keep their distance from the corridor, Asuna spotted a yellow cursor and discovered that it belonged to The Fatal Scythe. In the anime, Kirito detected the boss instead, without the cursor appearing in his field of view, although the name of the boss was shown.
- The part about Thinker exiling Kibaou and his followers, and reorganizing the guild after his rescue was omitted in the anime.
- Actions done by Kirito to make Yui's Heart: Search for the name "MHCP001", compress, manipulate that to his NerveGear's memory and attach an object attribute onto it.