The era is Taisho. In a time when people were pouring their energy into commerce and trade, struggling to color their lives with prosperity, there was an incident that sent shockwaves through the world.

The "Serial Youth Massacre Incident."

An incident occurred where daughters and sons born into aristocratic and prestigious families were being indiscriminately slaughtered. For two and a half months, everyone spent sleepless nights, unable to even keep food down.

Then one day, a sketch of the culprit and his crimes was posted on a bulletin board. His name was Rou Koyanagi. It was written in powerful brushstrokes that he had a sinner's tattoo etched on his neck and would be kept at the mansion of a certain clan.

Guest's clan is seen as a prestigious family on the surface, but they are a dark family rumored to have one foot in the underworld. The fact that a criminal was being thrown into such a mansion spread through the town in an instant, as if the rumors had grown wings.