As Zidane, go up the stairs and talk to the princess.

After an episode with Zorn and Thorn, you'll get to name Steiner. As soon as you gain control of Steiner, talk to the Queen to receive an item based on the number of nobles you impressed during the mock swordfight:

Go into the knights quarters and talk to the 2 knights (Blutzen and Kohel)there. Grab a Phoenix Down near the door. Go out and north to the main hall, follow the balcony to the right and enter the dining hall. Give Mullenkedheim the order and then exit. Catch Dojebon as he runs around the balcony. Go downstairs and into the left library. Talk to Laudo and then head outside to the courtyard. At the canal, talk to Haagen and the head to the right. Talk to the knight at the gate there and then head back left. Pull Weimar away from the girl and then head into the left gate. Go up the spiral stairs to find Breireicht. Talk to him a second time and if you found all the Knights he'll give you an Elixir. Continue to the top of the tower.

After the dramatic chase scene, you'll be Zidane on the Prima Vista. Chase the princess down to the meeting room. After jumping down to the engine room, turn the wheel to the left and to the right, then go down the stairs and pick up the two items that fell: a Phoenix Down and Phoenix Pinion.

When you enter the next room, Steiner (I) will catch up and Zidane has to fight with the help of Cinna and Blank. After the battle, Zidane, Garnet and Steiner will do a little improv onstage. Then Vivi runs onto the stage and another battle with Steiner (II) ensues, this time Zidane gets help from Garnet (Dagger), Vivi and Marcus. After the second battle is over the Prima Vista takes off, but the Queen launches harpoons and a Bomb to stop it. A third battle with Steiner (III) starts. After a few rounds he finally notices the Bomb just as it explodes, causing the Prima Vista to crash into the forest.