The Parella are a Minor Faction in Hyrule Conquest's Great Sea expansion.
The Parella are the most loyal and oldest servants and leaders of the dark god Bellum, and the River Zora of its previous conquest, whom serve as the military branch. Bellum employs lesser creatures to do its bidding as well, though the Parella and River Zora are its favorite since they can take and hold land targets.
Pre-Dawn of Hyrule
Many millions of years before the creation of Hyrule, the Parella's homeworld was attacked by Bellum. In order to avoid being devoured, the Parella adapted a mutualistic relationship with the beast. They would build the Mirror Gates to constantly direct Bellum from world to world, conquering or assimilating native species, while ensuring that Bellum would have a steady source of food so it wouldn't turn on them. The Parella would eventually come to incorporate the River Zora as their servants when their homeworld fell victim to it.
During this period, one of the worlds targeted by the Parella was the Realm of Twilight, which was still an ocean planet back then. Bellum killed most of the native life and reduced the planet to a dark, bleak, cold wasteland.
Dawn of Hyrule
With Hyrule in its infancy, the Parella heard the call of the First Sages and directed Bellum to the newborn world, where they formed an alliance with the First Sages and the other Druthulidi. Bellum crept into the primordial oceans that had only barely formed. The Parella recruited more followers from the primitive ocean life, waited for the oceans to rise and built more Mirrors to reinforce their armies. The Parella along with the Druthulidi later betrayed their First Sage allies, and after the First Sages allied with Majora to deal with them, Bellum, the Parella and their minions retreated to the depths of the ocean or to other worlds where the enemy could not pursue them.
Around 4700 BG, the Parella instigated a war between the Oshus Empire and Cobble Kingdom. They aided all three sides in the war until being exposed, causing the Oshunites to reject any further help. The Cobble Kingdom, remaining loyal to their Parella allies, used their help to dominate most of the land and sea north of Hyrule. When the Phantom Army was unleashed by King Oshus, the Parella-Cobble alliance was kept at bay and eventually defeated, before the Phantoms turned on their creators and destroyed them. Bellum retreated to the deeps and entered a deep sleep while more Parella armies on other worlds prepared themselves.
During this time, the Parella genetically enhanced a group of their River Zora servants to create a new race which would be called High Zora. However, this experiment ended up a failure as the High Zora betrayed the Parella, moved south to continental Hyrule, pledged themselves to the Oshunite exile Jabun and founded the Zora Dominion.
When Archon Jelyf attempts to lead a group of Parella back to Hyrule, they end up in the Realm of Twilight: it turns out that this portal has been tampered with by the Gerudo, when they banished the Dark Interlopers from Hyrule. Jelyf allies herself with the Twili king Mizorant and his son Zant, offering to open portals into Hyrule and aid in conquering the land; although in reality, she only wishes to use him as a tool against the Zora Dominion, and alerts the River Zora princess Sokuuf about her incoming arrival.
Once the Mirrors are completed, their destinations are set to the capital of the Zora Dominion. After using their Twili allies as a distraction to bomb Domain Prime, the Parella and River Zora head north to the Great Sea to continue locating Bellum.