And I would love to tell you. @spiiderbiites
Fun fact: It does have a name, Deep Seas and High Stakes, but I am pretty sure it’s going to be tagged on both blogs as Mermaid AU That Needs a Name forever, because there were a lot of posts made with that tag, and even though tag replacer is a thing, so is laziness. Also, SOMEONE keeps forgetting the name. It’s me. I am someone, even though I came up with the name. I blame the fact that the title does not reference anything and isn’t a joke. It’s just “what sounds like a swashbuckling adventure romance mermaid and pirate au title?” title. The AU’s real name is Bless the Woodpecker anyway. Don’t ask.
Once Upon a Time, Eraqus and Xehanort ruled the Kingdom Below, comprised of the seas surrounding the Destiny Islands, together, the wisdom and magic of both rulers renown even in far off seas . Then there was a big, gay, magical, underwater divorce a falling out. The stories say it was over King Xehanort's dabbling in dark arts, though other legends place the blame on King Eraqus's xenophobia and King Xehanort's belief that the denizens of the surface world could be easily manipulated negotiated with. This argument took a darker turn when the trident that they shared (a single conduit of unmatched strength that represented the harmony of their rule and their bond) was shattered, and with it, a large portion of both Mer-kings' power was lost.
Eraqus retained rule and loyalty of their subjects and Xehanort was banished to deep trenches to nurse his grudges and seek still more twisted ways to rebuild his power. Good King Eraqus himself, suffering from broken heart and diminished strength, survived not long after (in mer terms) but it was not his wasting that killed him, but human menaces, cementing the lesson that the most dangerous creature of all in the mind of the young princess now queen, Aqua.
Hatchmates Sora, Vanitas, Roxas, and Xion were eggs when the big, gay, magical, underwater divorce falling out happened and small fry when Eraqus passed, but they have heard far too many versions of the story. We don't talk about how the royal siblings came to be. We just don't. Don't ask. Magic was involved. IDK. "I Will Do Anything for Love but I Won't Do That" will start playing in the background if you start talking about seahorses and try to lock down details.
Anyway. Fast forward to the hatchmates grown.
Vanitas has always been an outsider among his siblings, or at least he's always felt it. He's drawn to different currents, and his siblings don't understand, citing their own restlessness and desire to explore and to lead less sheltered lives when he tries to explain how his purpose lies elsewhere. He seeks out the only other family that he might have a connection with, Xehanort, and ends up staying with him to become his apprentice. Queen Aqua and his other siblings do try and go after him at different times but they are thoroughly discouraged by Vanitas himself.
Kairi, princess of a different sea kingdom, comes to live with our royal family. She's a gift--a description Kairi herself highly resents--a future wife for one of the princes, part of an arrangement made long ago. The marriage isn't to happen for a long time; she is allowed to get to know the princes and they her, and see what personality suits, but that is far as the freedom goes as Kairi's kingdom needs the alliance and the young Queen Aqua is regrettably convinced she cannot dissolve or alter the contract without incident. Kairi and Sora do hit it off immediately, so the choice would seem easy, but they are both still far from enthusiastic about the forced aspect of it all.
Life under the sea is really shaken up though when rebellious Prince Roxas, long time sneaky boat chaser, meets a sailor named Axel and is struck dumb in love. He starts disappearing more and more often and it doesn't escape notice. Even worse, this "human madness" spreads, Prince Sora and Princess Kairi both independently becoming obsessed with Axel's crewmate aboard the Dawnfire, Riku. Xion does not feel the same kind of bolt but she is convinced of Axel and Riku's good intentions and to keep this "hatchmate secret" from Aqua.
Ventus, a dreamer who was first to start weaving tales of mermaids even though he's not met any, and, the solid, reliable Terra, who Axel and Riku don't dare tell about their liaisons with the deep for fear of being laughed at in the best case and put in an asylum at the next port at worst, round out the crew of the Dawnfire.
Xion finds what she thinks is a match of her own when she follows the music of a "land siren" one day and meets Demyx. Unfortunately, Demyx and Xion are not as sneaky or as lucky as some others, and Demyx runs with a rougher crew than Axel and Riku. Xion's Land Siren proves as dangerous as his nickname implies when Xion finds herself caught in a trap of the infamous Thirteen ( a pirate crew that is admittedly down a few numbers from what their name implies, which we blame on frequent mutinies) and then used in turn as bait for a bigger catch after Demyx is caught meeting with Xion by Xigbar and bullied into betraying her trust.
Why do they want the mermaids? Sell off mermaid scales as having magical and medicinal use when used as potion ingredients. Harvest mermaid tears. Sell the mermaids themselves to a sideshow. All valid reasons even if you discount that some larger plot may be at play.
What happens next? That's spoilers for one day when writing cute, funny scenes about Sora and Riku breaking down the language barrier or drawing Axel and Roxas snuggling isn't more pressing.
The mermaids aren't the only prisoners aboard the Thirteen's vessel though. There is also the fair Namine, a nobleman's daughter kidnapped for the ransom, though she is treated with far more accommodation.
Just put tagged/mermaid au that needs a name in my or Shaky’s blog for more, or ask more questions if you want.