Main Walkthrough

Location: The Hideaway (ship)
Petitioner: Clive's Reading Desk
Unlocked: Begin Back to Their Origin and complete An Inconvenient Truth
Reward: Stolas Quill, Bahamut's Mercy, 30 Renown

In order to unlock this side quest you must first complete two prerequisites:

  • You need to progress through Back to Their Origin, one of the final main quests in Final Fantasy XVI. It will have you speak to several NPCs in the Hideaway. Once you're done talking with Jill a bunch of new side quests will pop up.
  • You need to complete An Inconvenient Truth. It is one of the side quests that appear in the Hideaway during Back to Their Origin.
Check Clive's Reading Table and you'll find a missive from Harpocrates. He has a favor to ask regarding Dion, prince of Sanbreque, and he requires Clive's help. Agree and you'll need to pay Harpocrates a visit in the Shelves. 

Speak to Harpocrates and you'll discover that he and Dion have some shared history. Harpocrates wants to procure a wild wyvern tail, a type of flower, for the prince. Harpocrates knows of only one place where they might grow, and that's over in Ash, near Eistla.

Fast Travel to Eistla - the Shadow Coast will also do, if you have access to a Chocobo - and trek to the Angry Gap, the bulbous swamp in the south of Waloed. Make your way to the western section of the swamp and check in the northeast, near the thin paths where the two halves of the Angry Gap connect. 
There's a waterfall over here... 
..and it is guarded by an Akashic Lindwurm. Great. The Lindwurm fights the same as the other, many wyverns that you've fought over the course of the game, with the main difference that it uses no fire attacks. Expect only claw swipes and charging body slams. Defeat the Lindwurm (and any other enemies who may stray into range) and you can collect some Wild Wyvern Tail from the flowers by the waterwall. 

Take the flowers back to Harpocrates, then fetch Dion. He's standing on the upper walkway of the Boarding Dock. Speaking to him will trigger a cut scene and end the quest.

Main Walkthrough