Youko Nakajima has always wanted nothing more than to be ordinary. She follows instructions, earns high marks, serves as class president, and lends a hand to classmates whenever possible—yet her red hair has always made her stand out as different. Because of her passive nature, Youko lets others take advantage of her, leaving her with no one she can truly consider a friend.
Then, on what seems like a normal day, a man claiming to be from another world bursts into Youko's classroom and kneels before her. This refined, blond-haired man named Keiki declares that Youko is his liege and destined to rule his kingdom. But their encounter is abruptly interrupted when youma—monstrous beasts from another world—pursue Keiki. He manages to flee with Youko into his own realm, but two other classmates, Ikuya Asano and Yuka Sugimoto, are swept into the chaos as well. Their troubles are far from over, as the youma attack leaves them separated from Keiki. Stranded in this unfamiliar world, these ordinary students must learn to survive on their own or face death.