How to Complete Pirate Attack

The objective is to defeat Grayrl before he boards the ship. The other enemies in this battle, which you can ignore if you wish, are a Moogle Knight, three Vikings, an Archer, and a Black Mage. The law forbids harming Humes, so if you do not want to break the law, don't attack the Archer or Black Mage (or any of your own Hume units, if any).