Sesami of the monster-control crew has been dispatched to Eventide Island, where he has found three pirate strongholds.
Quest Location
Talk to Sesami on the north end of Eventide Island at 4513, -3501, 0001 to start this quest.
How to Complete the Quest
You have to defeat all of the Monster Forces on the three strongholds on the island, then enter Eventide Island Cave around the back of the east end of the island and defeat the pirates on the ship there.
Quest Reward
Talk to Sesami after you have defeated all of the pirates and he will give you a Blue-Maned Lynel Saber Horn.