Youko Nakajima has strived for a mundane existence. She follows orders, maintains high grades, leads her classmates as the president, and lends a hand to those in need. Nonetheless, due to her crimson locks, she has never blended in. Along with her subservient demeanor, Youko allows her peers to exploit her, leaving her friendless. Unexpectedly, a foreign man bursts into Youko's classroom one day, claiming to hail from another realm. Keiki, an exquisite fair-haired gentleman, deems Youko his rightful ruler and insists that she ascend the throne of his kingdom. Unfortunately, their initial encounter ends swiftly due to the presence of nefarious creatures called youma who pursue Keiki. After fleeing with Youko to his world, two other students, Ikuya Asano and Yuka Sugimoto, undergo the same chaos. Regrettably, the youma onslaught caused them to split from Keiki. Stranded in a surreal territory, these ordinary teenagers must adapt to their hostile surroundings or perish.