(A/N quick Universe lore; Atypical= person who can turn into an animal. Standalone= an Atypical born with a non-Atypical twin)
Pietro was a Standalone. His sister, bless her heart, was unbelievably jealous the first time Pietro shifted when they were four.
That jealousy quickly disappeared when Pietro let her ride on his back while he ran around.
He had always been proud of his second form, a sturdy, elegant snow leopard with blue eyes and sleek fur. The Cheetah of the North, his mother had always teased.
After their parents died, it was up to Pietro to keep him and Wanda safe. They were bounced around from foster home to foster home until the state tried to separate them. That's when they ran away.
The streets of the city were unforgiving, and they took to a life of thievery to stay fed.
After years on the street, they just barely managed to claw their way into the workforce, and finally got an apartment.
But, somehow, Pietro's boss found out his designation and fired him, and then told any employer he could about it, giving them a picture of Pietro.
They lost the apartment, Wanda couldn't support them both on one paycheque, and any place Pietro tried to give his resumé slammed the door in his face.
They were on the streets again when HYDRA found them. They took them in, with promises of work and board, told them that if they partook in an experiment, they'd be rewarded.
Pietro spent the first few weeks flitting about in his cell, electricity in his blood, begging them to let him talk to his sister.
They called him Quicksilver, and he was their weapon. They trained him, held a gun to his sister's head had him kill people, politicians, polices officers, activists. They kept saying, 'One more job, Quicksilver, then you can see your sister'.
Their first mistake was actually letting them see each other. Pietro was pretty sure he'd cried.
They hadn't trained a gun to her head, they hadn't killed her and then sicked him on their little problems. No, they had done something much worse. They made her into their weapon, they made her like him, a killer.
They took his poor, innocent sister, who would never hurt a fly, and ripped her apart, held a gun to his head and made her into the Scarlet Witch. They had played them both.
HYDRA's second mistake was allowing them to room together, Pietro took the top bunk, Wanda the bottom, and in the darkness, they whispered plans in their Super Secret Twin Language.
They would send Quicksilver out on missions while the Scarlet Witch trained, making sure he knew they weren't afraid of killing one of their best assassins if he ever stepped out of line.
Not that Pietro ever would, he was loyal to HYDRA. After all, they were their saviours, weren't they?
HYDRA's last mistake was sending Quicksilver and the Scarlet Witch on a mission together.
They killed their team and ran as fast as they could. Or, rather, Pietro briskly jogged while carrying a screaming Wanda.
They laid low, keeping to the shadows, they were on the streets again, but the streets were better than killing just because you were told to. A year after they had escaped, nearly four since they got their powers, they caught sight of a news broadcast on a bar's TV.
They watched with relieved grins as the news anchors declared the outing of HYDRA. HYDRA needed the darkness to survive, they thrived off of ignorance. They would never last in the light of day.
They were in New York City when they were found once again, but instead of HYDRA, an Avenger saw Wanda shoplifting, and took her in when she tried to use her powers to escape.
Pietro was half-mad with worry when Wanda didn't come home that night. The next day, however, a silly-looking blond man with a bow and arrow stood at the door of the apartment they were squatting in.
"You the redhead's brother?" He asked harshly.
Pietro blinked "Why do you want to know?" He asked.
The blond smirked, as though he already knew the answer "I arrested her yesterday," he said, leaning casually on the door frame, "Your lucky our Alpha's Mate has such a soft spot for stray's with haunted eyes, he's practically adopted her."
Pietro relaxed slightly "You're an Atypical?" He asked conversationally, cocking his head.
The blond hummed, "You got a problem with that, kid?"
Pietro laughed, grinning to show off his sharp canines "Not at all,"
The blond stood straighter, hostile demeanour melting away like wax. He held out a hand, "Clint Barton, nice to meet you, Wanda's been talking about you all day,"
Pietro grinned, shaking the offered hand "I know who you are, you're an Avenger. And how do you know I'm not just a random squatter?"
Barton huffed, pushing himself off of the door frame "The accent's a bit of a give-away," he teased, gesturing for Pietro to follow him "C'mon, let's not keep Wanda waiting, she scares me," he said, shuddering.
Pietro followed without complaint.
This time, when they were offered a job, they were told from the get-go that they'd have to fight anything from robots to HYDRA agents. They gladly signed on.
The Avengers didn't seem to care about their past or the fact Pietro was Atypical.
Pietro was only two sentences into his first conversation with Anthony when the man declared that he was adopting him. The others only sighed, muttering about the odds of twins.
Banner didn't judge when Pietro was caught making out with a man he'd met at a bar, though the Hawk didn't look particularly happy when Pietro strolled into the kitchen the next morning with a bruise on his throat.
The Avengers supported them, though and though, slowly becoming family
Barnes told them about his time as a weapon, that they weren't alone, and that HYDRA sucked massive dick. That day they stopped calling him Barnes, and he became Uncle James.
When Rogers, the Alpha of the Pride, came to him asking about Atypical culture in Sokovia, and Feline culture in general, Pietro had laughed while beckoning him over.
"Oh you poor thing, two wolves and a hawk, and none of the elegance of a great cat," he said.
Wanda snorted. "Elegance? I've seen you run face-first into walls,"
Pietro had pouted while Rogers stifled a laugh.
Pietro taught Rogers as much as he knew, which was quite a lot after a decade of sleeping and showering in the homes of Atypical's lucky enough to work at an international company.
Rogers seemed surprised that people trusted Pietro just like that, but Pietro had explained that Atypical's in Sokovia played to the Camaraderie Law like nobody's business. Very fortunate for a stray Standalone and his sister.
After their impromptu cultures lesson, and much insistence from the Captain, Rogers became Steven.
Romanova taught Wanda and Pietro how to braid, using Thor as her example piece, while the twins worked on the much thicker hair of James. While Pietro and Wanda carefully wrapped a hair tie around their braids, Romanova calmly told them that if they didn't start calling her Natasha she would be very upset.
Given that they really didn't want to see the scariest woman they'd ever met upset, Romanova became Natasha.
It was while Banner was helping Anthony with their suits that he told them they could call him Bruce. Very straightforward, they liked that about him.
Pietro and Barton were on their third date when he told him to call him Clint, a fact that Wanda never let them forget.
It was while Wanda was making fun of Pietro for calling his boyfriend by his last name, while the others lamented about how long it took for them to get on a first-name basis with the twins, that Thor chimed in.
"I was never called anything other than my given name by the twins," he said, frowning.
Pietro shrugged "We don't know what your last name is,"
Thor nodded firmly "And now you never will,"
Wanda laughed "Don't be such a child, Odinson," she chastised.
Anthony snapped his fingers "I smell a liar!"
Wanda nodded sagely, "Ah, lying is wrong, no?" She said, leaning back in her seat "Perhaps we just like Thor the most,"
Wanda got a pillow to the face for that comment.