I might change this later don't take it as strict canon

Ah, forests were nice. Peri's childhood was spent hopping between tree branches and building snow forts, so this brought a sense of nostalgia.
I still don't know how this place works, but there are others here. Maybe they know what's going on.
The dimension had a strong, but foreign magical energy. It wasn't something Peri was used to, and the magic was clogging their senses. If Peri came to a dimension that had strange magic, it could interfere with their nerves and make them go blind, deaf, or worse. One of their senses usually stayed behind, however, and they used whatever was at their disposal to get around.
As they ran through the snow, they came across a huge, gnarled, tree. Feeling a bit tired, they hopped easily into a branch for a quick catnap. (pun intended) Not wanting others to disturb them, they stopped trying to have a form, and dreamed.

The familiar forest brought back buried memories, it seemed. Some might say nostalgia, but Peri knew better. Nostalgia was the longing feeling for something you lost, and Peri longed for nothing from her days as a young child.

How long had it been since they slept? As they were a Void creature, they had no need for sleep, food, or water, since they weren't technically alive. This didn't mean they didn't like eating or sleeping, but they didn't need it. Peri did need routine, however, and made it a point to sleep at least a few hours a week and eat every other day.

Even though Peri wanted to sleep, they didn't like it. Like how a high-schooler doesn't like taking tests, but they know they need to to pass school. Peri found their head was clearer after a nap, even if their dreams were bad.

Peri's sleep was restless. Being in the familiar woods brought up bad thoughts. Once again, they began to fall into the mind track of a weapon.
After all, Peri's entire purpose was to be a weapon. A force of destruction meant to destroy anyone standing in their way. Their physical powers were strong, and they were created to be a mindless, emotionless, killing machine. They were not meant to have family. Their father CREATOR did not care for them and did not see them as a child who needed a parent.

Creator gave them sustenance, a place to sleep, and education.

Peri did not have comfort. Peri did not have companionship. Peri did not need food, or water, or sleep. Peri wasn't even really alive.

Weapons did not need love. Peri did not know what love was.

They didn't want it. How can you miss what you never had?

If Peri never experienced love, how could they feel love? As they were incredibly emotionally underdeveloped, they were expressionless and almost sociopathic.

One day, Peri fell ill.

Creator could not diagnose the problem. They began to consider the very likely scenario that Peri would die.

Peri had been around for a solid 10 years, and had made much progress in combat, education, and was a smart and well developed (about as well as they could be) weapon. Creator didn't want to lose all their hard work. They poured all the healthcare they knew to heal Peri. But they weren't getting better.

Creator took DNA from more of the ancient species and made another weapon. On accident, the developing embryos split. There were now twins.

Creator admitted to the King what they had done, but the King told them to raise both weapons the same as he did Peri. The king didn't understand that the reason Peri was emotionless and cared for nothing was because they had no one. Having a sibling would give them something to care for and talk to. Creator tried to explain, but the King wouldn't have it. 2 weapons were better than 1, right?

One day, as the twins were almost ready to be removed from their growing space, Peri woke up. This was bad. Creator had not planned for Peri to survive, but they decided to keep all 3 weapons apart, so they could be raised as originally planned. The plan was for none of them to know of the other's existence until they were older and could form a team.

Well, as Creator should have been prepared for, things don't usually go as planned.

When Peri was healed, Creator continued them on a strict training regimen, while the twins were born. The plan was to separate them as soon as they were removed, but one twin was smaller and weaker physically, but had immense magical power. The other was healthy and strong, but less magically powerful. Even before they were really conscious, they relied on each other, and Creator found they couldn't be separated without constant crying that went on for weeks. The twins had to be raised together.
As Peri was the first, they were the prototype, and aged as a 10 year old should. Not wanting to spend 10 more years on the new ones, they aged while developing, and were born as around 5-6 years old. Still easily moldable.

Peri knew nothing. They were still recovering from their illness, and slept a lot.
One day, while they were reading a chemistry textbook, they heard a strange sound coming from the air vents. Crying? One emotion Creator was not able to stomp out was curiosity, much to his annoyance, which was why Peri read college level textbooks. Peri could not shapeshift yet, so instead of slipping through the grates, they slipped out through the door. Walking down the twisting hallways, Peri found the source of the crying.
Two small kittens, like them. Grey fur, like them. Cute little paws with claws and tail and ears, like them. Tiny bird wings, like them. Why were they making that strange whining sound? Why was water coming out of their eyes? WHY WERE THEY SO SIMILAR?

Sitting down to observe them, the two kittens didn't notice Peri at first, too preoccupied with their crying. The tests that were done on them were painful to a young child, and it was just instinct to cry. That instinct wasn't stomped out by Creator yet, and Peri felt a sense of awe. Reaching out to touch one, the smaller one looked up and noticed the older cat. Instead of screaming and running away, they reached out as well and touched paws.

It was blinding.

The smaller kitten was physically weak, sure. It was clumsy and got sick easily, but was smart as a whip, like Peri. Even though it only had brainpower to fight with, they also had immense magical power, like Peri. When they touched paws, Peri, who had never touched another magical being (Creator wasn't magical) wasn't used to it.

The larger kitten was strong, stocky, and healthy, but it's magical power was...less than stellar. Creator's plan for this one was for it to be the smaller one's shield, while the smaller one dished out magical attacks. Brains and brawn, if you will. The larger kitten, always optimistic and happy, joined in the impromptu group hug.

The connection was instant. When they separated, Peri knew in their heart that they were siblings. Nothing Creator did could keep them apart now.

"I'm Peri. Who are you?"
The younger kittens didn't have names. Peri's full name was Peregrine, after they found a large book of birds and matched their wings to that of the peregrine falcon. Creator didn't like that much, but put up with it.
"I'm One. This is Two." The smaller kitten answered.
"Do you want different names?" "Yes, but we don't know any other names," the larger kitten said.

Well, this won't do. They're so sweet, they deserve real names. Peri went back to her room, retrieved her book of birds, and came back. The kittens hadn't moved. "I have a book of birds. I picked my name because my wings look like a peregrine's," they said, pointing to the page with the favored bird. Peri sat back and let the kittens flip through the book.
"Ooh! Ooh! That's me! My wings are like that birdie's!" The larger kitten exclaimed. It was pointing to a picture of a hawk. Sadly, the larger kitten couldn't read, so Peri said, "Okay, your new name is Hawk." The smaller kitten purred, flipped through the book, and pointed to a page. The average house sparrow. "I'm Sparrow." Sparrow could apparently read.

Peregrine, Hawk, and Sparrow. A perfect trio. Creator was angry when he saw them together, but the ball was rolling, and nothing could stop it. Soon after, Peri had escaped, and took the small kittens with them. While they were being chased by the military, Sparrow jumped in front of a stray attack headed for Hawk, and was killed.

Peri and Hawk made it out safely, but Sparrow's tiny body had to be left behind.
What no one knew was that since the kittens had spent their whole life together, their magic relied on each other as well. Hawk actually didn't have enough magic to survive on their own, and borrowed it from Sparrow. Now that Sparrow was gone, Hawk died soon after.

The project had failed. Peri grew up all alone. Living as a feral cat in the forest amplified their powers, and when they were found, they couldn't be brought back. Peri became a dimension hopper. Their new life began.