This book is a novelization of Akagami No Shirayukihime. Akagami No Shirayukihime is a Japanese anime called "Snow White With The Red Hair" in English.

It's finally time for Shirayuki and Obi to return to Wistal castle when all of a sudden prince Zen's comes to them, what for? Later Izana, Zen, and Shirayuki are summoned by King soba of Crystalia to participate in a tournament where the prize could just be the secret Shirayuki has been hiding