In this world, here are two kinds of intelligent beings. One are humans and the other are Diaboliques. Diaboliques possess power, violence, intelligence, and eternal life. Their life form was categorized into four levels, the lowest division lacking intelligence, reproduction ability and beauty and the fourth being very intelligent and able to change form.
For thousands of years, human race has been suppressed by the danger of diabolique. However, a legend has passed on through generation that there's diabolique that kills its own species. This diabolique was Azulite - one of the only five Road Diabolique (the ones of highest category). Being known as the "species killer," Azulite has come up to kill diaboliques. At here, he met a girl named Letticia. Her innocence and tragic background has attracted Azulite, and soon Azulite fell in love with her. However, the two lovers were separated after Letticia was killed. They promised to see each other when she was reincarnated. Carrying with the promise, Azulite once again set off on a journey looking for Letticia.