3x3 Eyes

Through a strange series of events, a young man named Yakumo Fuuji becomes the immortal slave of the last of a race of 3 Eyed immortals. The immortal, Pai, absorbs his soul to save his life, making him immortal in the process. Now, he begins a journey with the female immortal in an attempt to find a way of becoming human. Of course, there are many complications along the way, not the least of which being that the immortal is a female with a split personality, one achingly cute and the other being no-nonsense destructive power, and romances that develop between. (Source: MyAnimeList)