Ragnarok

Ragnarok (ラグナロク) was the ruler of the Fourth Realm who was brought through the portal of the Black Rose, by the Cult of Diablos to gain his powers.

Appearance
He had the appearance of a bluish-black demon with an enormous body like the demon king Diabolos, with a fanged mouth, have 4 sharp claws with each extending from the tips of his long and thick arms like blood, strong legs with 3 toes each, and his whole body was enveloped in flames accompanied by a pair of very large wings from which he can fly.

Personality
Ragnarok even though he is a magical beast and a demon king, his behavior seems almost the same as that of an animal that acts almost by instinct, he attacks when he wants to sometimes, and when provoked. Shadow described him as a being who does not have much of a brain, comparing him to Delta, since he does not exercise his magic or does not know how to handle it well.

Being a rather simple-minded magical beast, the Cult of Diablos found a way to partially control him for their benefit.

Background
When the Black Rose incident occurred, the demon king Ragnarok had the opportunity to briefly appear in Oriana Kingdom but was repelled by the Cult of Diablos, who were very interested in the phenomena of the so-called "Black Rose" and that there is more than one world, apart from the one inhabited by the people of the world where Cid reincarnated, (this was long before Cid reincarnated).

Through a treaty that was made between Oriana's past kings and the leaders of the cult, a calamity was avoided thanks to the cult. But, in exchange for the royal family having to hand over their royal daughters, since Oriana's royal family has a bond of blood with the human Heroin, and the kingdom were to give a majority of their tax revenue to them, resulting in the kingdom to heavily invest on the arts. Also, the cult manipulating the church to vilify their kingdoms Dark Knights and the kingdom basically became a cult's puppet.

Oriana's "Black Rose" Civil War Wedding Incident
Ragnarok is summoned again to the magical world where Oriana's kingdom was there, through the "Black Rose" portal using the "Ring of Succession" that Rose Oriana wore at her wedding, which was really the key to activate "the Black Rose". Then, it begins to generate chaos but quickly loses one of its wings at the hands of Shadow, and they begin fighting to the death outside the capital, which ultimately results in his death at the hands of Shadow as he cutting every demonic members that falls near the battle that Mordred had against Epsilon, Beta, and Rose, who was watching how they fought.

Powers & Abilities
Ragnarok possesses brute strength, magical power, and ferocity that almost rivals the demon king of Diabolos. But, it seems he doesn't have the ability to quickly heal his wounds and isn't smart enough to use his magical power on himself.

It is speculated that using his magic could rival the demon Diabolos and being the king of the fourth world of demons, he must have ruled there with sheer insane strength.

Even though he is not that smart, Ragnarok has the ability to shoot bursts of magical power from his mouth like a dragon and from his wings as well.

Trivia

 * The name Ragnarok itself is interpreted as a natural disaster that comes from Norse Mythology.
 * When Shadow annihilated the demon king Ragnarok leaving only one of his members, he did it in a similar way to Olivier when she cut off one of the arms of the demon king, Diabolos. But, the difference is that Olivier defeated him with the help of her fellow heroes, while Shadow did it alone.