3x3 Eyes is an action-horror series based on the popular manga by Yuzo Takada. It revolves around Yakumo Fujii, a Japanese high school student, and Pai Pavarti IV. Pai's outward appearance is that of a ditzy high school girl. However, she shares a split personality as a Sanjiyan named Pavarti. The Sanjiyan are a race of powerful magical beings with three eyes.
While the lifespan of a Sanjiyan is extremely long in comparison to humans, they can still be killed. Thus, they can take other creatures (including humans) and make them into a protector called a Wu. By linking their souls, the Sanjiyan grants the Wu immortal life as long as the Sanjiyan lives. But if the Sanjiyan dies, then the Wu also dies. Pai turns Yakumo into her Wu in order to save his life.
However, Yakumo is not well-suited to being a Wu, as all it gives him is immortality. It gives him absolutely no inherent magic or fighting ability -- many of the blood and guts seen in the first series are Yakumo's. But for those who have seen the first series, rejoice because Yakumo has since learned to kick butt.
Despite the supernatural horror aspects, 3x3 Eyes is also a romance. Through protecting each other, Yakumo and Pai fall in love. At the end of the first series, Pai has a confrontation with Benares, the Wu of the Sanjiyan KaiYanWan, to protect Yakumo. In the ensuing fight, there is a huge explosion, and both Benares and Pai disappear. The first series concludes, and the second series begins with Yakumo searching for Pai.
Yuzo Takada is also the creator of Nuku Nuku and Blue Seed. Coincidentally, the seiyuu for the lead of these three series (Nuku Nuku, Momiji, and Pai) is the omnipresent Megumi Hayashibara. Those of you who have seen Kishin Heidan may note similarities in the music between that series and 3x3 Eyes II. The soundtracks for both series were composed by Kaoru Wada.