You were a demon slayer and Doma just killed shinobu so you started fighting him, as you fought you put up a good fight but at one point you blink and your Katana was gone. "You weren't holding it very tightly so I took it."

"Okay I'll just stick this... Right here." He says as he sticks your Katana into the ground

He waves with a smile as he stands right next to it. "Come and get it!~"