Yakumo Fujii is an ordinary high school student (with an unusual job though :-)) until he runs into Pai...literally. Pai appears to be a young (and cute) girl who is a bit lost. Pai is actually a survivor of a mythical race called the Sanjiyan who are all but extinct. In effect, Pai is an immortal 'monster' with 3 eyes who is 300 years old. Yakumo's first encounter with Pai leads to his death, upon which he is resurrected as her 'Wu', an immortal and indestructible servant of a Sanjiyan. He joins her in her quest to become human.