Due to a bizarre chain of events, a young man named Yakumo Fuuji becomes the immortal slave of the last member of a race of three-eyed immortals. The immortal, Pai, absorbs his soul to save his life, thereby making him immortal as well. He then embarks on a journey with the female immortal, aiming to find a way to regain his humanity. Naturally, numerous complications arise along the path, most notably the fact that the immortal possesses a split personality—one side achingly cute, the other a no-nonsense force of destruction—as well as romances that develop between them.