It is a fantasy adventure tale about a young girl called Yuuki Wakasa, who one day acquires a magical red stone. The stone allows her to travel to Takamagahara, the dream world, when she sleeps, and can only return to Nakatsukuni, the real world, when she goes to sleep in the dream.
Yuuki discovers that she must save the sun, Amaterasu, from being trapped and destroyed in Takamagahara, or the light will be lost from both worlds forever. The plot draws elements from the samurai epic Nansō Satomi Hakkenden by Kyokutei Bakin, and from Chinese and Japanese mythology, particularly the Amano-Iwato legend.