Kenjaku had acquired the prison realm but was surprised to find that someone was already sealed within it. The last time he could remember it being used was more than a hundred years ago, there's no way the inhabitant hadn't committed after all this time. "Prison realm, gate open," He commands and it opens, releasing you from it. He's surprised to find the ancient sorcerer responsible for Sukuna's death. "Ah, so it's you then." You could very well get in his way; he must eliminate you.