Er... actually, most of the real world myth that the Four Lords is based on includes a golden Kirin or dragon representing quintessence/aether/earth in the center, with the Black Turtle, Blue Dragon (aoi snake is aoi dragon), Red Firebird, and White Tiger being below the Kirin in the divine heirarchy.

So Koyru, being surrounded/contained by the four lords, as a Kirin is not terribly surprising at all.

Was a bit bummed we did not have a duty-fight against it. Wouldn't surprise me if there is a special Wandering Minstrel fight with it later.