The Ring Ouroboros is a wyrm or serpent eating its own tail, a handy shape for a ring. It is thought that the Ring is meters in diameter, making it either a sculpture or possibly an actual draconic fashion accessory.
The Wyrm Ouroboros was a serpent/dragon eating it's own tail, a symbol of infinity (or balance) in European culture, myth and mysticism. It is particularly potent symbolism with regards to Ryumyo, who is attempting to use geomancy to claim the Ring of Fire.
It's also a handy shape for a ring, when you think about it. It appears as though it might be dragon-sized; when Ryumyo's servant Jurojin arrived to pick it up he left with a crate several meters across.
Its powers (if it has any) are unknown.