Quote Originally Posted by Itsunari 2000
There's a 13th stellazio coin :Ophiuchus ... though it's been so long since I finished the stellazio quests I can't seem to remember exactly where I got it ...
I believe the 13th Stellazzio is back at Quan's Dwelling, perhaps on the shore bordering the hot springs. It only appears once you've given the other 12 Stellazzio to Queen Stella and she's given them back to you momentarily to go nab the 13th.