Pai looks like any young girl, but is really the 300-year-old last survivor of the Sanjiyan, an ancient race of three-eyed demons that were destroyed in a war with Kaiyanwan, their own leader. In addition to being immortal themselves, the Sanjiyan hold the coveted secret to immortality. Pai, however, wants nothing more than to become human. When she runs into Yakumo, an average high school student, she ends up with no choice but to turn him into her Wu--an immortal servant tied to her as long as she remains a Sanjiyan. As the two of them search for a way to make both Pai and Yakumo human again, they will both have to grapple with just what that means. And the search is not an easy one: There are dark forces seeking to extract the secret of immortality from Pai.