When you do the opera house, do a speed run, and skipped two rats. After beating them, leave and continue as normal. Get Setzer and go back to the opera house. Go to the balconey, and there will be two rats still there! Fight them and after winning the battle, you will see the scene of the octopus dropping the weight. Afterwards, you will get a blank screen, and you will appear outside in the world of balance. When you go inside towns, it's in the ruin version. Also, if you take the castle, your airship will leave, and you'll be back in the world of ruin. You will have to restart your game after this.