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Cordial Chords (コーディアル・コード, Kōdiaru Kōdo?) is an extra story written by the author of the Sword Art Online light novel series, Kawahara Reki. It was released with the Japanese Limited Edition Blu-Rays and DVDs of Ordinal Scale, and is a sequel to the events of Hopeful Chant and Ordinal Scale.
On May 7, 2026, Kirigaya Kazuto and Yuuki Asuna were spending their lunch break in a difficult-to-reach green zone their school's campus. With his girlfriend sleeping on his lap, the boy gently caressed her hair as he contemplated on how the sensation of hair, among other things, was handled in games. Having suddenly awoken in the midst of his musings and discovered where she was lying, Asuna attempted to rise to her feet due to feeling embarrassed. However, she was stopped by Kazuto, who urged her to sleep a little longer, arguing that they still had twenty minutes of their break left, while Doctor Kurahashi had stated that sleep would accelerate her recovery from the memory scan conducted on her. Despite showing some resistance, the girl once again lay her head on Kazuto's lap, before returning to sleep.
Kazuto recalled the scepticism that the Augma was met with when it was announced, due to being developed by a company that had specialised in social networking games and video streaming services, rather than being a manufacturing company. For most people, these doubts were completely eliminated with the release of Ordinal Scale, a game that had attained tremendous popularity upon release due to a variety of reasons. However, Kazuto remained suspicious, as the technology employed for the Augma to allow it to send visual, auditory, and limited tactile signals into the user's brain was far too advanced for company that had just entered the industry. Although the announcement that the Augma's development was spearheaded by Kayaba Akihiko's mentor, Professor Shigemura Tetsuhiro, explained how the company was able to develop such advanced technology, it did not abate Kazuto's cautiousness.
Then, at the end of April, Kazuto discovered about the professor's plans to use Ordinal Scale to scan the memories of Sword Art Online (SAO) survivors in order to use their memories of his daughter, Shigemura Yuuna, to recreate her as a digital ghost. The professor was thus able to create «White Yuna», an Artificial Intelligence (AI) with his daughter's personality and limited memories, based on the language engine of An Incarnation of the Radius, the monster that was meant to serve as the final boss of Sword Art Online before it became a death game, and the collected memories. However, as the personality of the AI was too accurate, it assisted Kazuto and the others in defeating the boss in order to stop the professor's plans before it could kill a large number of SAO survivors, despite knowing that the defeat of the boss would result in the AI itself being deleted.
However, even eight days after the incident, Kazuto could not stop thinking about two things. The first was Nochizawa Eiji, Shigemura Yuuna's childhood friend who had been helping with the professor's plans. Due to the bodily injury Eiji had inflicted to the members of Fuurinkazan, Eiji had surrendered himself to the police two days after the incident and was still being detained, though he was likely to avoid prosecution due to the Fuurinkazan members not pressing charges against him. The other was YUNA (Black Yuna), the Ordinal Scale image character and Augmented Reality idol, who possessed a simpler personality than White Yuna and was still working as an idol. While Kazuto felt it unlikely to meet either of the two ever again, he believed that he would not be able to forget them so easily.
That afternoon, while contemplating on his and Asuna's commutes to school, Kazuto returned home. There, he was greeted by Kirigaya Suguha, who had returned home earlier than usual. Discovering that his cousin was secretly eating some ice cream, the boy persuaded her to share some with him, before going to his room. There, Kazuto noticed the Augma lying on his desk while considering doing his homework. Although the device had not been confiscated by the government and was still popular, since the truth about the incident at YUNA's concert had been concealed from the public, while the memory scanning feature had been eliminated, Kazuto decided to stop using the Augma nonetheless.
Having equipped the device, the boy, just as he was about to format the Augma, noticed a push notification on the device's virtual desktop with a reference to Yuna. After tapping on the message by reflex, he discovered that it was an announcement for a new YUNA desktop mascot application for the Augma. Driven by the curiosity, the boy installed the application in order to say his farewells to Yuna. While the little YUNA mascot did not seem unusual at first, shortly after Kazuto gave it his in-game nickname, the mascot suddenly glitched, pleading for his assistance in a serious tone, before returning to normal just as abruptly.
Confounded, the boy pondered on the mysterious message. As YUNA was now the property of Kamura and her data had been reset, he concluded that only White Yuna could have sent the message, meaning that she could possibly still be found in the old SAO server. Due to not knowing Professor Shigemura's whereabouts, Kazuto decided to instead call Kikuoka Seijirou for information on the only other person whom he could question about Yuna and the SAO server. Just as he finished the call upon acquiring the information he needed, the boy heard Suguha calling him for a dinner.
On May 7, seven days following his surrender to the police, Nochizawa Eiji was released from the Yoyogi police station without indictment, due to no one pressing charges against him. Standing within the premises of the police station, Eiji considered his next course of action. He was reluctant to return to his apartment, as this would result in him returning to his life of despair. This made the young man recall how he had secluded himself in an inn on the 1st Floor ever since Yuna's death in Sword Art Online. His days were spent agonising about what he could have done to prevent the incident, gradually beginning to blame the other members of his party, especially the two members from Fuurinkazan, for Yuna's death.
Having been kept alive by the faint hope of Yuuna being spared, Eiji became only more depressed upon returning to the real world, only to discover that his hopes were in vain. As his parents had divorced and cared little about him, Eiji decided to continue living alone in seclusion. His dreary life in despair lasted until he was one day contacted by Professor Shigemura Tetsuhiro, who gave Eiji reason to live again by inviting the young man to help with a project to resurrect Yuuna in the form of a digital ghost.
However, as their plan had failed while the man whom he had trusted deeply had betrayed him, Eiji no longer had a place to go to after being released from police custody. Lacking a goal, Eiji deliberated wandering aimlessly through town to avoid returning home, when he noticed the man he least wanted to see waiting for him in front of the station upon leaving the premises.
Having learnt that Yuuna's death was similar to the demise of the «Moonlit Black Cats» guild in its circumstances, Kazuto felt he understood the antagonism expressed by Eiji upon seeing him, as Kazuto himself had shown similar attitude towards Asuna and Klein after the death of his guild. Before he could even greet Eiji, the latter demanded to know his reason for coming to see him. In order to avoid attracting unnecessary attention, Kazuto proposed moving to a nearby family restaurant before answering his question.
After placing their orders at the restaurant, Kazuto informed Eiji of the existence of a YUNA desktop mascot, adding that Professor Shigemura had transferred the rights to YUNA to Kamura and a company named «Ario Room». Kazuto then revealed that the mascot had pleaded for assistance.