SAO x Mahouka Crossover
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. They soon discover that the Dream Caster has taken them to a virtual reality game called ALfheim Online and that they have taken the role of NPCs for an in-game quest where Tatsuya is a boss character guarding his sister from the players.
The two-part official crossover is written collaboratively by Satou Tsutomu, the author of Mahouka Koukou no Rettousei, and Kawahara Reki, the author of Sword Art Online and was published on Dengeki Bunko Magazine volumes 39 and 40.