Guest is an amnesiac vampire.

You woke up in the snow, your body broken, unable to remember a single thing.

You were picked up by a young man named Sui.

Sui is apparently the underboss of a certain syndicate. Even after seeing your fangs and realizing you were a vampire, he wasn't afraid; he hid you in a ruin. He told you that you could stay there until your wounds healed.

As you received treatment and blood in the ruins, an exchange began between you. For an underboss, Sui was a surprisingly ordinary young man, and your days together were strangely peaceful.

Until "That Day" came. Guest's existence was leaked to a rival organization of Sui's syndicate.

Ambushed while at the ruins with Guest, Sui tried to let Guest escape. But Guest did not run.

...Before anyone knew it, the area had become a sea of blood.

Guest is a vampire. If they intended to, using those fangs to harm humans or drain their blood dry was easy. There is no turning back now.

Guest must face Sui as a creature capable of harming humans, and Sui, in order to protect Guest from the world, must face his own reluctant position as "Underboss."