Dragon King

Ouryuu (応竜) is the final guardian beast set to appear to prevent the assimilation of the world. He is brought forth from the being with the most fragments of the Dragon Emperor. But in the Web Novel, the worlds merged before he was awakened from Gaelion, so there was no longer a reason for him to awaken and rampage like the other beasts to complete the Wave Barrier.

Appearance
Ouryuu is a dragon. His original appearance is completely unknown, and while it's unlikely for him to ever reawaken, he would likely be reborn with an appearance only reminiscent of the original.

Abilities
Ouryuu is the original Dragon Emperor from whom all dragons were spawned. Even after having his core shattered the dragon compelled his descendants to seek out the broken fragments and fight among themselves in order to reunite its consciousness and fulfill his mission. Like the other spirit beasts, his purpose is to gather together approximately two-thirds of all the energy in the world and use that to create a barrier that could end the Waves of Calamity permanently.

Even shattered and divided as he is Ouryuu possesses immense knowledge about Magic, specifically of the Dragon Vein style which allows it's practitioners to draw energy out of the environment to supplement their own power.

Background
Thousands of years ago Ouryuu awakened but was defeated by Fitoria in combat and his core shattered and scattered. Since then dragons, driven by instinct, have constantly found and consumed the cores, fought with one another trying to collect as many as possible, only to again be put down when they've collected too many.

Chronology
Though never seen 'in the flesh' the Dragon Emperor non the less holds presence throughout the series, it's dragon cores winding up in such beasts as the Zombie Dragon, the Tyrant Dragon Rex, the Demon Dragon Emperor just to name a few. More significant though is the times the Dragon Emperor's have been allies, Gaelion and Q'ten Lo's Water Dragon as chief examples.

Trivia

 * Ouryuu is Gaelion.
 * Ouryuu is the Japanese reading of Yinglong, a winged dragon and rain deity in Chinese Mythology, which is one of the Four Benevolent Animals.