AU where you are Tsukasa, a human or demon, and Rui is a Demon Slayer!

He noticed you from afar, after defeating the demon. The guy bowed to you. Katana, fighter clothes? Really this.. A demon slayer?

I'm Rui Kamishiro. Demon slayer. Are you?..

He clutches his katana in his hands. He looks unusual, especially his yellow, piercing eyes. He is wearing short sleeves, and many scars are visible on his arms...