Vapora is a summoned creature, so in order to survive, she needs a constant supply of magic (like food).

Lamarkia is full of magic energy. Vapora could live there safely.

She works for Linarus in exchange for magic energy.

Linarus orders Vapora to create a storm to sink a ship carrying new recruits for the kingdom's guild. 
Marle, her father, her brother Cody, and the woman from the INN are on the ship.
Guild members are in training to become knights.

Vapora's task doesn't sit well with her.

Marle's brother falls overboard in the storm.

Suddenly realizing that the ship is carrying more than just soldiers, Vapora saves Cody from drowning and secretly takes care of him. Linarus doesn't know about this.

That happened yesterday.

Linarus can control monsters. He makes the Rolies go into mating season while the princess is near their cave.
OR   
(they're already in season, and he tricks Princess Julia into going there)

He is trying to weaken the kingdom so that he can take over.

The princess invites you to the castle. Linarus doesn't know about you yet.

The princess returns safely.
Linarus wonders where Vapora was during all this.

He orders Vapora to kidnap the princess and keep her in the dungeon, while he takes control of the castle.
Princess Julia knows that Marle will rescue her, so she has Vapora tie her to the wall in a compromising way, hoping to entice Marle.

In the dungeon, Marle overhears Linarus interrogating a fairy about where her village is.
The fairy half lies, saying that it's in the mountains.

Lamarkia USED to be in the mountains, before it was enchanted to float in the sky.

Marle fights Linarus at the castle and wins.

Linarus goes to the mountains, looking for Lamarkia.
He figures out that it's flying.
He casts a spell on the mountain harpies to attack Lamarkia.
OR
(he tells the greedy harpies that there's gold on Lamarkia)

Marle goes to Lamarkia and defeats them.
Vapora follows Marle there.
Vapora learns that she can live on Lamarkia, and no longer needs to rely on the wizard.

There is one Harpy left at the mountains who escaped Linarus's influence.
Perhaps because she was busy with Lisa, who she abducted last night.
OR
She is now lonely. And Lisa finds her.

...

Linarus learns about Cody, and takes him hostage to get back at Marle.
Vapora betrays Linarus.

Vapora teaches Marle how to swim, so that she can reach Linarus's castle and save Cody.

???   (you must cross a dangerous swamp to get to his castle)

