Orthros Reise Arnor was born to the first of the emperor Valius V's secondary wives, daughter of the Cayenne Dukedom.
- Main article: War of the Lions
Following the death of his father, Valius Reise Arnor V, and assassination of his half-brother, Crown Prince Manfred, Prince Orthros, seized the Imperial capital Heimdallr by force. Once in control, he declared himself the new emperor and began purging all those who dared to oppose him.
To give himself the upperhand against the armies of his half-brothers, Orthros revived the Testa-Rossa that had once been sealed away by Emperor Hector I underneath Heimdallr. This brought about a shift in the balance of power during the civil war. With its unmatched strength under his control, Orthros decimated his greatest competition in one fell swoop, and the fifth prince, Gunnar, was defeated.
It seemed inevitable that the armies of the other princes would share the same fate, but it was at this pivotal point that the war took yet another surprising turn. This unexpected development came in the form of another Divine Knight: The Palatinate Knight. The famed champion was acquired by Prince Lucius, the sixth and youngest of the feuding brothers. Prince Lucius was poised to challenge Orthros.
In S.952, Orthros felt pressured by the combined force of Prince Dreichels, the warriors from the Nord Highlands, the Eisenritter under command of Lianne Sandlot, and the Palatinate Knight of Prince Lucius. Prince Orthros schemed to elevate the cursed Vermillion Knight to even greater power, and created the Vermillion Apocalypse.
The demonic god emerged in Heimdallr alongside the Infernal Castle and vanquished the approaching armies of Princes Albert and Gunnar in a single battle. Even the Palatinate Knight could not contend with such a foe and felled. And as it decimated all who challenged Orthros, countless crimson spirit veins spread out from the castle, stealing the very life from the capital's citizens, as well as those in the surrounding area.
With the Ashen Knight in Dreichels's possession, along with their many supporters and the army of Prince Lucius, they marched on the capital for the final time, eventually making their way to the Infernal Castle at its centre.
Three days later, on July 4th, S.952, Orthros was defeated by Prince Dreichels. The Infernal Castle vanished from existence and the Heimdallr was liberated. The fact that Orthros was a descendant of the Cayenne Dukedom's bloodline was hidden after the War of the Lions came to a close.
During the Erebonian Civil War in S.1204, Orthros's descendant Cayenne tried to realise Orthros's dream by unleashing the Vermillion Apocalypse upon Heimdallr once again. Like his ancestor, Cayenne did also not succeed in taking over the ruel of Heimdallr.
- It is unknown whether Emperor Orthros was officially acknowledged as Emperor of Erebonia by the state at one point in time.