In my quest to Legendary Stylist, there are a lot of small quest to complete. One that’s really been giving me trouble is finding the last Stoneheart!

Here are a few notes that have helped me.
Healing each spire should spring a quest where you help a piecys that’s been “stuck” since the skypass is closed and they haven’t been able to fly out.
The Map shows where stonehearts are located (outlined in purple).
On the ground/sea level, under the Barrel Grove Warp spire

Between the Handsome Lads Circus and Market of Mirth Summit Path Warp Spires

Near the Choo-Choo Station Stonetree Top Warp Spire

Near the Stone Steles Warp Spire

Near the Windrider Mill Top

The quest to heal each Tainted Stonedew Flora pops-up when you are in the vicinity of the Stoneheart in question.
You’re looking to get rid of esselings through the assorted quests that have attacked the dew source for the Stonehearts: Stonedew Floras.

I had the hardest time finding the last one for me, the Windrider Stoneheart (Quest: Repair the Windrider Mill Skypass); Admittedly, I didn’t understand the map helps me find them and the 5 are on the small islands around the main island.
After what felt like too long, I completed it under Advanced Courses: A Kaleidoscope World

Gallery of images from completing my final stoneheart quest. It had a cutscene and everything.