The Irregular at Magic High School: Appendix (Light Novel)

It's September 2095. A certain package has been misdelivered to the First Magic High School of Japan, and it contains a "Relic": a piece of magical technology produced by an unknown civilization. And without anyone knowing, it automatically starts up... When Tatsuya Shiba comes to, he was in the woods. Perplexed by the dream-like world he found himself in, Miyuki appears before him. He's relieved that his little sister is safe and that they were able to reunite... But when Miyuki puts on a snow-white dress, she begins to completely change into the daughter of the king?!