Since Arthur's eighth birthday, Merlin had made him promise that anything written in the Harry Potter books was out of bounds, so naturally Arthur, as was his wont, found other inspirations to royally screw Merlin over.
"You want me what!?" Merlin put eloquently and looked down at the serious face of just turned eleven-year-old Arthur.
Arthur pouted slightly, and crossed his arms. "As my birthday present, I want you to be my dæmon," he repeated, stubborn.
Merlin blinked. "Is this the revenge for me vetoing to use a Flying Charm on your skateboard for the fourth time in a row?"
"No!" Arthur said, but he refused to meet Merlin's eyes. He colored slightly, but continued. "You're going to transform back to an animal again anyway for another year after today. Why can't you be my dæmon instead, I'd want to see what you'd be when you settle!"
Merlin bit his lip. It was true that since Arthur's rebirth, he had only allowed himself little over four years (and Arthur's birthdays) to take care of Arthur before he'd forced himself to leave permanently. Merlin had lasted almost a week before he'd come back as a dog. Well, a working week, anyway — or at least the majority of it. But Arthur had been crying himself to sleep, and only four and a half at the time. Merlin could not keep away, but at the same time Arthur had to learn to live on his own and acquire age appropriate friends without a thousand year old wizard hovering constantly over like a battle ready Apache helicopter.
So Arthur had loved Merlin as a dog, as a turtle, as a miniature pig, as a wallaby, as an owl and even as a baby acromantula (for a very short while though, after a regrettable eighth birthday present incident). There was no doubt that Merlin wouldn't be taken care of as a what-ever-it-was —and anyway he was immortal as thoroughly verified during that acromantula incident.
"What exactly is a dæmon, anyway?" Merlin asked cautiously.
Arthur's face brightened considerably. "It's brilliant! I read it from a book," he said, which should have set alarm bells ringing straight away, because Arthur had a terrible way of taking things literally, especially literature. "Every person has one, it's their pet animal shape shifter and when they grow up, the dæmon settles to an animal that best suits the person's character. I bet mine would be big!"
It sounded surprisingly doable, even for one of Arthur's infamous birthday wishes. Merlin almost considered it, but experience had made him wary. "How big is big exactly? And is that all there to dæmons?"
"The biggest one I remember was a snow leopard," Arthur responded. To Merlin's raised the eyebrows he gulped and confessed to the floor. "Your dæmon can talk with you without any else hearing it. And the dæmon must be close to the person all the time." He blushed furiously, and refused to look at Merlin.
It was a bit embarrassing how quickly Merlin fulfilled that particular birthday wish after that.
Being Arthur's dæmon was surprisingly brilliant.
Merlin had missed speaking with Arthur, and while Arthur had talked to him, he had started to be over the age where talking aloud to animals was still cute instead of the first sign of insanity. And being constantly close to Arthur was a definitive benefit — on top saving the world twice from disasters that only Arthur could bring into existence.
Naturally they fought over the form, as Merlin liked himself small and unobtrusive whereas Arthur preferred big and exotic. Merlin's changing form was the real manifestation to what the household had been conditioned to living with Arthur, as no one batted an eye to the parade of horses, lions and baby elephants around Arthur's rooms.
It was only when Merlin discovered Arthur fondling the Encyclopedia of Dinosaurs and Prehistoric Creatures with glee that he realized exactly the amount of trouble he was in.
Before he had not paid much thought to what animal he would ultimately settle into, but even as a child Arthur was nothing less than an once and future king on top of being born of Magic, and thus Merlin doubted that he would come out of the settling as anything smaller than a hippopotamus.
And as proved eleventh and a half months later, he wasn't exactly wrong.
Because of course, of course, Arthur's dæmon could not settle into anything less than a ninety ton magical beast, a golden dragon that could breathe fire.
"Cool!" beamed Arthur with pride, evaluating Merlin with eyes shining from happiness, not all disturbed by the debris in his hair, the utter destruction caused by a sudden appearance of new exits on his bedroom and the smoking pile of ash in place of his bed.
"Can you fly?" Arthur asked, ecstatic.
Had he not feared collapsing the whole western wing, Merlin would have banged his head against the nearby wall.
Merlin almost didn't forgive Arthur for managing to score a flying vehicle anyhow, but really, the last straw was Merlin needing to use the bloody Obliviate of all spells as a means to fix the disaster.