There are 6 final Owls to track down and return to the Owl Forest once you reach the endgame for Tales of Arise. These are completely optional but offer multiple Trophies/Achievements while granting you rewards mostly in the form of cosmetics.
How to unlock the final 6 Owls
In order for the final 6 Owls to appear in Dahna, you must first have found all 32 and seen both events at the Owl Forest, along with receiving the rewards from the Owl King. You must then progress the story until you set foot on Rena, at which point you’ll obtain a notification that the final 6 Owls have appeared in Dahna.
Owl #33 - Calagalia - Glanymede Castle - Lord’s Chamber
Make a return to Glanymede Castle and head up to the Lord’s Chamber where you first encountered Balseph. Take a look on the throne itself to find this oversized Owl and obtain the Battle Maiden’s Shield.
Owl #34 - Calagalia - Iglia Wastes
Return to Iglia Wastes and climb the landmass to the southwest where you found the first Owl here. You should see a raise area to the north here and now that you’ve learnt Dohalim’s Map Action, you can create some vines to climb it. The Owl itself sits on the rocks to the right of the red chest and will hand over the Vivid Sphere.
Owl #35 - Cyslodia - Riville Prison Tower - Hidden Chamber
Return to Cyslodia and the Riville Prison Tower, and make your way to the Collection Room. From here, pass into the Office and then finally the Hidden Chamber to find the Owl perched on top of the display case to your left, this one presents you with the Broken Machine Gun. You’ll need to ensure you’ve completed the Culling the Snowplain Herds and Survey Says… Sub-Quests to obtain the key needed for the Hidden Chamber.
Owl #36 - Menancia - Autelina Palace 2F - Guard Room
A return to Autelina Palace is next on the agenda, make your way there and head to the Guard Room on the 2F. You’ll find the Owl on a desk along the northern wall, this Owl will hand over the Ancient Excavator.
Owl #37 - Ganath Haros - Del Fharis Castle - Lord’s Chamber
A simple Owl to locate, simply return to Del Fharis Castle’s Lord’s Chamber (which conveniently has a Fast Travel) and look on the throne to find it. This one will present you with the Trident.
Owl #38 - Uninhabited Island
The final Owl requires a bit more work before you can access it’s location. To begin with, you’ll need to begin and complete the Beyond the Grave Sub-Quest, this won’t be present on the map so you’ll need to enter Tuah Seashore to trigger a scene and start the Sub-Quest. Once started, you’ll need to head to the Hidden Wharf and speak to Mahavar to have him take you over to the Uninhabited Island. Once on this island, you’ll find the boss of the Sub-Quest to the x which is Lv 59 so you may need to wait until you can best it. Once defeated, look to the rocks on your left to find the final Owl that will hand over the Metal Miner’s Cap.
The Owl Forest Reward
Once you’ve found all 38 Owls, return to the Owl Forest and speak to the King to trigger some Skits and obtain the Machine Beast Statue, Owl King Doll and unlock the Owl Homecoming Trophy.