|Spoiler Alert: This article or section contains details about plotlines not covered in the anime. Do not proceed unless you wish to be spoiled. |
Versus II (バーサス II, Bāsasu II?) is the second and final part of a crossover story between the Sword Art Online and The irregular at magic high school series. This part of the crossover was written by Kawahara Reki, the author of Sword Art Online, supervised by Satou Tsutomu, the author of The irregular at magic high school, and published in Dengeki Bunko Magazine volume 40. This story is a sequel to Dream Game -Crossover- and Versus.
A week after the encounter with Silver Crow during a test with the Soul Translator (STL), and several days after encountering Shiba Tatsuya in ALfheim Online, Kirigaya Kazuto (Kirito) was having breakfast with Kirigaya Suguha, when she asked him to explain what a quantum computer was. Although Kazuto was hesitant, once Suguha apologised for her question by saying that there were things that Kazuto did not know either, Kazuto agreed to give her a rough explanation.
Kazuto first explained the difference between quanta and elementary particles by using rice grains and their energy value as an analogy. He then explained what a Neumann computer was and stated that such computers had difficulty in decomposing large numbers into prime numbers. Finally, he explained how a quantum computer would be superior to a Neumann computer, as it could process multiple tasks simultaneously via superposition. However, to Kazuto's dismay, after he finished his explanation, Suguha bluntly stated that she did not understand the explanation.
Later that day, Kazuto came to his part-time job in Roppongi and complained to Higa Takeru about Suguha not comprehending his explanation. After Kazuto calmed down, he asked Takeru whether the STL was capable of decomposing very large numbers into prime numbers. Takeru claimed that it could not, but admitted that he had tried tried improving the STL to win the prize for deciphering an RSA encryption until his actions were discovered by Kikuoka Seijirou and he was scolded for it. Takeru then changed the topic, as he wanted to begin the test. While waiting for the test to begin, Kazuto recalled how he had encountered Silver Crow during the previous test and thought how the event could have been caused by the STL using quantum registers in parallel worlds, resulting in the two quantum devices interfering with each other. Kazuto ended his thoughts with the conclusion that he could not verify this, as such an event was unlikely to occur again.
Kirito found himself inside a pure white sphere, instead of a forest where he should have appeared. Although Kirito had asked to use a default avatar, he found that he looked exactly like his avatar in ALfheim Online. Just as Kirito voiced his complaint about the situation, he heard another person responding to him. Kirito was about to draw his sword when he realised that he had already met with the person before. Although the man wore a school uniform that Kirito had no memories of, he recognised the man as being the mysterious character who had taken the role of the giant Beli in a quest in ALO.
After Tatsuya explained that they were inside a virtual simulation, he decided to tell Kirito his real name and then considered whether he should take the same measures to deal with his own world connecting with Kirito's. However, Kirito claimed that there should be other measures that would overload the simulator and break the connection. Kirito then recalled his conversation with Suguha in the morning and came up with the idea to have the simulator decompose a very large number into prime numbers. He began flying by using his fairy wings and, after Tatsuya followed him, Kirito shared his idea with Tatsuya. However, to Kirito's shock, Tatsuya handled the decomposition via mental arithmetics in a brief moment, causing the world to collapse.