(If the inclusion of the arms on a shield with supporters is against the rules I can reupload with just the banner alone. I kinda got carried away.)
The North Sea Empire
Imperium Mare Septentrio
The successful regency of Hakon in Norway for Canute the Great can be said to have been the true key to ensuring the strength of the North Sea Empire. With his loyal vassal deftly ensuring the loyalty of the local jarls and helping to create a steady chain of resources between the three dominions of England, Norway, and Denmark, the empire began to solidify, though many rebellions would occur throughout its history. Canute the Great would focus his reign in England, but through Hakon and later through the half-English Ulfred, his other kingdoms would fall in-line, and when Canute began to tour his territory in his later years, he found a kingdom that was "not united, but together," a phrase which would define the North Sea for many years to come. When Canute died, his sole surviving son Harthacanute would succeed all his titles, but uprisings in Denmark would require him to rally his vassals in both England and Norway to successfully pacify the unruly Danes. Truly, it was not until the crown was eventually placed on the brow of Hakon IV that the North Sea Empire was truly 'unified,' as he was the first to style himself as 'Emperor of the North Sea, King of England, of Denmark, of Norway,' dropping the traditional title 'King of some of the Swedes' used since Canute, and under him its borders reached and solidified those established by Canute the Great after many years of the Empire's gradual shrinkage; for the majority of its history, the North Sea Empire was focused in England, having to fight tooth and nail to keep its footholds in Norway and Denmark, ironic as that is. And the people within the Empire, though separated by sea, survived long and grueling wars, before finally achieving true supremacy with victory against the French and the North Swedes under Hakon. Now together, the maritime nation would then begin using its thalassocratic nature to its advantage, building many ports and encouraging enlistment of all in either civilian or military naval forces. Many a philosopher has remarked that often there are more citizens of the North Sea in its waters than on its lands, and though hyperbolic, they are nearly right, particularly in times of war or invasion."
- History in a Second by Reinaldo Cortez
"The arms of the North Sea Empire are derived from the ancient 'Raven Banner' of many Norse pagan lords. A black raven on white would serve to inspire images of Wodin, the most feared and powerful of their gods, king of their pantheon. Though the North Sea Empire would convert almost entirely to Christianity, the marching of its armies under the Raven became a part of its shared history, and such a disparate kingdom was constantly urged to embrace all common features by its government. Eventually, the House of Knýtlinga, without its own arms for over two centuries, despite the trends in Europe, would take a crowned black raven on white as theirs, later augmented with a border of red to represent the nature of the empire, being a united kingdom in a vast space of both earth and water. Today, the raven has become increasingly stylized, an action taken in response to the Teutonic Republic, the resulting counter-revolutionary movements emulating their obsession with simplified symbols as a means of uniting their peoples before a revolution hit them...
...While not supplanting the civil and state flag, the royal banner was and is flown in all three of the Federal Kingdoms that lie underneath the title of Emperor of the North Sea. The capital of London flies the royal banner exclusively, without the red and gold English saltire beneath it, alongside the state flag, as it wishes to be an embodiment of Imperial unity, despite remaining feeling in much of the country that England is the most dominant and influential kingdom, at the expense of the other two...
...Officially the arms are supported by a wild man, taken from the Danish, and a golden wyvern, taken from the English, with the Crown of St. Æthelwulf, created and housed in Norway, resting above it, acting a symbolic uniting of the three lands around the House of Knýtlinga. The official motto of the Knýtlingas is "Deus, Iusticia, Pax," meaning "God, Justice, Peace," a phrase taken from Canute IX as his reasons for fighting for the North Sea, despite the belief that the Glorious Coalition of the Teutonic Empire, Iberian Popular State, and the Federation of France and Italy would never be defeated. Given the North Sea Empire's miraculous victory (with aid from the Serfdom of Vinland and the Kingdom of New Lombardy) the phrase became a popular part of the Septentrian national consciousness, and the imperial family made it their official motto rather than continue to have new monarchs establish their own upon ascension."
- The Little Book of Flags, by Javier Moreno