In the late 21st century, a subculture of humans have emerged who have been modified genetically by a vampire-like disease, giving them enhanced speed, incredible stamina and acute intelligence. As they are set apart from “normal” and “healthy” humans, the world is pushed to the brink of worldwide civil war aimed at the destruction of the “diseased” population. In the middle of this crossed-fire is – an infected woman – Ultraviolet, who finds herself protecting a nine-year-old boy who has been marked for death by the human government as he is believed to be a threat to humans.

The story is set in the early 21st century with the population decimated by bio terror. Two kinds of humans now exist. One is the Nokusu who were infected with a virus but survived and consequently they carry an antibody. Most are young, healthy and have high intelligence, but they have a high sensitivity to ultraviolet rays and are active mostly during the night. The other group are the Kyurio. They survived by never having the virus. The Nokusu discriminates against the Kyurio. Tetsuhiko Okudera is a Kyurio. He was born in a poor village. He isn’t happy with being a Kyurio and wishes he could be a Nokusu. Yui Ikuta is Tetsuhiko’s childhood friend. She tries to revive the poor village.