After finding Terra in Zozo and learning the fate of the Espers, you look for a way to infiltrate the Empire.

Go to Jidoor

After assembling your party and equipping everyone with Espers, go south to Jidoor.

Talk to the Impresario

Go into the large mansion in north Jidoor and talk to the Impresario. (Note that the Impresario is NOT Owzer.) When he leaves, go south and read the letter that he drops. There will be a cutscene that introduces a new character (default name: Setzer).

Before you leave the Impresario's house, check the pot in the upper-right part of the house to find a Tincture/Ether. Then leave Jidoor and go south to the Opera House.

Opera House

Be sure to save the game before you enter the Opera House.

Equip relics that protect against Imp and Muddle/Confuse. Also equip the Sprint Shoes relic. Remove all Relics from Celes, and don't equip her with the Ramuh or Kirin Esper.

In the Opera House, talk to the Impresario. After a cutscene, the opera will begin.

Back Stage

After the singing, you will be in control of Locke. Walk to the right, then down the aisle at the bottom right, then go south, then east, to go to Celes's dressing room. Talk to Celes.

As Celes, read the book on the table to learn your lines. Then go up and out on stage.

You have to sing the correct lines when prompted, and if you take too long, the game will automatically choose whichever choice the cursor is on, whether it is the correct one or not. If you make an incorrect choice, you will have to do the opera over again. Here are the lines:

1. Oh my hero.../O my hero...
2. I'm the darkness...
3. Must I.../Must my...

When Draco appears, talk to him once to start dancing. Follow him around, and whenever he stops, talk to him again. When the flowers appear, pick them up, then go north and walk to the end of the balcony, then press A. After this, just watch the rest of Act 1 of the opera.

When you're back in control of Locke, go down and read the letter. Then go south, down the stairs, then up the red stairs and through the north door to return to the seating area. Talk to the Impresario.

After Locke says "It's as good as done," a five minute countdown begins. Going into the menu does NOT pause the countdown. It will help if you equip the Sprint Shoes relic.

Go to the upper-right of the seating area and go through the door. Talk to the guy there, then flip the far-right switch. Go back to where the Impresario is sitting, then go through the upper-left door.

When you reach the ceiling beams, move quickly but not hastily. If you are careful, you can avoid some of the Sewer Rats/Sewr Rats/Stunners and Vermins/Goetias. When fighting these enemies, don't use any spells or Blitzes, and be sure to kill the yellow rats first, each individually. When the yellow ones have died, use multiple-target attacks on the grey ones if possible.

If you didn't make it before the five minute countdown ended, you will have to try again. If you made it before the end of the countdown, you will battle Ultros.

Ultros

Ultros is weak to Fire and Lightning. Use the Siren special attack if you have equipped someone with Siren (press Up in the Magic menu to use it). Gau's Bomb rage is highly effective. Alternatively, use his Templar, Stray Cat, or Gold Bear Rage. Ultros will counterattack with Acid Rain if hit by a Blitz or SwdTech/Bushido move. Note that Ultros does not have anything to steal.

After the Opera

Watch the cutscene that takes place after the opera. Afterward, you will be on Setzer's airship. You can talk to him to get him to go to Vector. You can heal up for free on his ship, and there is a merchant on board if you need Potions/Hi-Potions or anything.