Blue demon

However, when Pollux Alder set his eyes on the inside of cage No. 10, he was suddenly stunned! In the empty cage, there was only an unusually large knife. The blade was nine feet long and covered with rust. It looked like a piece of abandoned copper and rotten iron, unbearable to the eyes.
Apart from this, there was no one in the cell?
"Are you talking to me?"
Pollux Alder frowned and looked at the big knife, but what surprised him was that he could not see any spirit in the knife, and...