Ruby Dragon can be fought on the Island Closest to Hell. It is extremely susceptible to Meltdown. I guess over all it's hard to find clues that might not relate to more than one enemy.
It all seems so clear now that you’ve explained it! I think I got put off track by the word “Draconian”. Because the last FF I played was FFXV, all I could think about when I saw Draconian was Bahamut. And once I had it in my head I couldn’t get rid of it XD
I actually had completely forgotten about the Ruby Dragon though.