Welcome in a world where the existence of "Demon" called creatures faded into legends and myths. Hiding in the underground in -mostly criminal- groups to survive, only few humans still know about their existence.
They try not to stand out among humans and only very few people notice that the specials colors of their hair and eyes are natural.

One of them is special. He's half human, half demon, a creature that was hunted already thousand of years ago and mostly killed in childhood, so it won't become a too powerful danger. After the orphan was found in adolescence by a demon, he was taken to the "Red String", a demonic organisation where he found a home and a job. He worked himself up to a high rank.

As time passes, small groups arise among the organisations with demons, who think earth should be ruled by them again...