Go see the Narvick elder. You'll talk and he'll ask these 3 girls to help you.

At the top of each tower is sealed 1 of the pieces of equipment

The first tower is on the same island as Narvick

Here.

Make your way to the top and you'll meet and fight Gades. Very easy fight.

She'll have an idea to help you fight the Sinistrals

Go back to Narvick and get another girl

This is your next destination

You'll meet and fight Amon at the top. Very easy fight.

Go back to Narvick for the last girl

And go to this tower.

Daos will be waiting for you. You won't fight him though. Be sure to save before meeting him though because this is the point of no return. Once you're through this part, you have to finish the game.

He'll beat you up but Maxim will resist

After an energetic fight, Dual Blade will side with Maxim.

Daos will run back to Doom Island and the girls will produce a forcefield to contain Doom Island

Amon's been busy though

You'll go back to Portravia for repairs

Maxim and Selan will have a heart to heart talk

But monsters will start invading the city. Dekar will run in to save the day

You're on your way to Doom Island