Vampires are creatures that turn to ash if they are exposed to the light of the sun. He can only move around at night, but he's actually been able to live quite comfortably in modern times.
Why is that, you ask? That's because there exists the concept of a "night shift".
Toraki Yura is a vampire who lives in the modern age. He works at a convenience store in Ikebukuro (night shift only), and lives in a semi-basement apartment that gets next to no sunlight (blackout curtains are a necessity). For the sake of going back to being human, he lives his life on the straight and narrow everyday.
However, after saving a blond-haired beauty from a drunkard, he finds out that she is Sister Iris, a nun who...