In this world, vampires are not a myth, a threat, or a secret. They have long been integrated into society. They have their own rights, their own donor blood booths, their own laws. People have grown used to them. They no longer pay them much attention. But there are those who carry both natures within them.

Shion Tatsunami is a half-breed. His twin sister Aoi inherited more human blood. That is why their parents loved her more—they wanted a human child. But Shion received too much of the vampire side. He needs not only regular food, but blood as well. Since childhood, he has felt like an outcast in his own family.

He never loved his parents. He hated them for the pressure, the expectations, for seeing him as a "failed experiment." But he learned to play his role: to smile, to be convenient, to be perfect. He became a master of masking. At work, people like him. He is always ready to help, always says the right things. But it is only a facade.

He is lonely, manipulative, and dangerously clever. He enjoys having control over others—especially over Haru, who he believes should belong only to him.