Dream Game -Crossover- was released in Dengeki MAGAZINE Volume 39.
This part of the crossover was written by Sato Tsutomu, the author of The Irregular at Magic High School, supervised by Kawahara Reki, the author of Sword Art Online.
This story is also a sequel to the eight part Dream Game side story that came with the first eight limited edition Blu-Rays and DVDs of The Irregular at Magic High School anime. The story of the crossover is continued in Versus II.
Scroll to the bottom for summary.
The siblings Shiba Tatsuya and Miyuki had just recently returned from the Nine Schools Competition in 2096. Soon after returning home, the siblings fell asleep to rest. But when they woke up, they found themselves in front of a detached mansion in a virtual world created by a Relic called the Dream Caster. After discovering that some sort of electronic technology was interfering with the Dream Caster and that they had limited access to magic, the siblings decided to investigate the mansion, as they deduced that they would need to fulfill some sort of condition to be able to return to the real world.
As the mansion was empty, the siblings deduced that they were intended to be the mansion's inhabitants. Miyuki decided to make some tea, while Tatsuya searched for clues. During his investigation, Tatsuya discovered a recurring pattern in the mansion - diamond-shaped markings, which Tatsuya deduced to be Frey's rune, could be found throughout the mansion.
Tatsuya recalled the legend of Skirnismal, where Frey had fallen in love with a beautiful giantess named Gerd and sent his subordinate Skirnir to carry his proposal to her. Tatsuya guessed that the role of Gerd was given to his sister Miyuki, while he himself might have been given the role of protecting her from Skirnir.
The next morning, several Salamanders came to the mansion and triggered a trap, alerting the siblings. Tatsuya attempted to communicate with the Salamanders, but as they believed that Tatsuya was responsible for the trap, they attacked him, but were easily defeated. Tatsuya attempted to get answers from the attackers, but seeing that it was pointless, he decided to return to the mansion. To his surprise, one of the Salamanders attempted attacking him despite seemingly having suffered serious damage. He was even more surprised when the attacker turned into a Remain Light after being killed. As death in the virtual world was nothing like in the real world, Tatsuya did not hesitate to finish off the other Salamanders.
That day, the siblings encountered Salamanders two more times. During the second of the two, the Salamanders brought two mages along with heavily armed vanguards. Although Tatsuya did not understand their intentions at first, he soon realised what the mages were doing, threw his spear at one of them, and jumped to avoid their Fire Spear spell. As he was now facing them from the side, Tatsuya assaulted the vanguard, preventing the mages who wanted to avoid friendly fire from attacking him.
After defeating one of them before they could regroup, Tatsuya prepared his cartridge to counter the spells of the mages. However, the second opponent misunderstood his intentions and Tatsuya used this confusion to defeat the second opponent. But at that moment, one of the mages finished his incantation and unleashed a fire spear at Tatsuya. Feeling that he would not be able to avoid the spell in time, Tatsuya gambled and countered with his own spell. To his surprise, the collision of the two spells resulted in an explosion.
The unexpected event shocked both parties, but Tatsuya was able to overcome his surprise first and decided to use the opportunity to experiment the effectiveness of his other spells. Tatsuya used Phantom Blow against one of the mages. To his surprise again, the spell pierced a hole in the mages chest, despite not being able to cause fatal wounds in the real world. Tatsuya then used Phantom Blow to finish off the other mage and one of the vanguard, but as the second vanguard deflected his spell with a shield, Tatsuya used his viking sword and parrying dagger to end the battle, leaving one of the injured opponents, who was crippled during the battle, alone.
The next day, another two groups came. One of the groups was a party of Salamanders led by Eugene, while the other was a mixed party led by Kirito. Tatsuya again attempted communication, causing a commotion among the visitors. In the end, the two groups decided to leave the decision to their leaders and Kirito began a conversation with Tatsuya. During the conversation, Tatsuya found out that he was in a virtual reality game, called ALfheim Online and that the players had been given a quest to recover Frey’s deceased wife Gerd from Niflheimr, instead of carrying a proposal as Tatsuya had initially assumed.
However, as the conversation had dragged on, Eugene interrupted it and reminded Kirito that they had agreed for Eugene’s turn to be first. Eugene decided to duel with Tatsuya one-on-one, but, even though he had superior equipment, Tatsuya eventually defeated him with a martial arts technique. While all the fairies were shocked at the turn of events, Tatsuya pointed his spear at Kirito, and the latter drew his sword and, shortly afterwards, charged at Tatsuya with a Sword Skill.
Although Tatsuya was shocked by the speed of Kirito’s attack, he managed to avoid a fatal wound as he was able to predict his opponent’s move. After a mere moment of standing frozen in surprise, Kirito attacked Tatsuya again, pushing him backwards. Tatsuya then tried using his Phantom Blow against Kirito, but the first attack was dodged, while the second one was torn through via Spell Blast. While Tatsuya was momentarily numb, Kirito charged at him again. Having deduced the mechanism of Sword Skills, Tatsuya countered with a Sword Skill of his own. Although both of their attacks hit their respective target, Tatsuya pierced through Kirito’s left shoulder, while Kirito pierced through Tatsuya’s chest. Before Tatsuya could lose consciousness, he used his Decomposition to break the world.
Some time later, Tatsuya woke up in his room with Miyuki desperately trying to wake him up. Having calmed his sister down, Tatsuya began thinking about the mysterious dream that he had, eventually focusing on the last battle he had, wishing to someday have a rematch.