This back appearance is... "FFXV" official comic "FINAL FANTASY XV episode car basket" episode 13 # FFXV # FF 15
https://www.famitsu.com/matome/ff15/EPC_13.html...
https://www.famitsu.com/matome/ff15/EPC_13.html
Google translate
The 13th: the symbol of the shield of the king
Ambra "Do you have any information about Iris?"
Plainer "The way to hear gradually became a straightball ...."
Ambra "Everyone knows of course, but Iris' older brother is Gradio, the big bird's tattoo stand out!"
Prayer "It seems he carved a tattoo transmitted to the family of Amicitians when the preparation as a shield of the King was decided, Claraus who is also his father should have the same tattoo"
Ambra "Why are you drawing birds?"
Prayer "As an article, it is said that the custom made to depict the birds that fly in the sky with the same wings originated from the wing dragon · Enkidou of Gilgamesh's partner, the shield of the first king. Perhaps it represents a respect for gilgamesh, which is said to be the shield of the strongest king. "
Ambra "For girugamesh and Enkidou, play with" FINAL FANTASY XV EPISODE GLADIOLUS "......, it turned out to be a story of the Amicitian family rather than Iris!"
"Final Fantasy XV" Famitsu.com Special Site> FINAL FANTASY XV Episode Carbuckle> "FINAL FANTASY XV Episode Carbuncle" episode 13