After the first prince Dominic was captured, he was immediately taken to a special cell with various magic formation. This cell was created by the emperor himself with the intention to trap even a supreme rank powerhouse here.
But even with his best efforts, he had not been successful in his plans. Actually trapping a supreme rank powerhouse anywhere was almost impossible. Someone might be able to do that but only with the help of the will of the universe.
But even then, the Otrefiona Emperor was at least able to create one of the toughest cells of the universe. Even if this was not something that could keep a supreme in, anyone who did not have the strength of a supreme could only dream about getting out of here.
