Fire And Ice - Yin and Yang (Harry Potter fanfiction)

First time at Hogwarts

Dear Professor Dumbledore,

I have just brought my boys to the Hogwarts Express and saw two little twin girls aboard it, not much older than four. They both had black curly hair and green eyes, as far as I could tell.
I do not know if they were meant to be on the train, but I thought I ought to inform you in case you might hear of worried parents looking for their daughters.

Best regards,
Molly Weasley

Professor Dumbledore slowly stroked his beard in thought as he lowered the letter.
"Twin girls", he mumbled and gazed down at the parchment. "With black hair and green eyes..."

The gold and red bird on the perch across the room trilled softly and gave him a curious look.

Professor Dumbledore suddenly smiled and looked at the phoenix over his half-moon spectacles.
"Fawkes, would you mind checking the Hogwarts train if there are two little stowaways aboard it? They will be most likely in the last compartment, barely anyone uses it."

Fawkes spread his wings and sung another melodious tune, before he disappeared in a yellow flash of light.

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Many miles away, Periwinkle moved slightly in her sleep when a bright warm light suddenly filled the compartment. She did not wake up and neither did her sister, but her hand instinctively moved to the warm shiny thing. Her little fingers wrapped around something soft and Periwinkle pulled on it, clutching it to her chest.

A student who walked past the last compartment of the train saw a bright yellow light shine through the crack of the door into the hallway. But when he slid the door aside, the light disappeared and there was nothing there.

He shrugged and kept walking towards the bathroom.

————————————————————

A few minutes later, Professor Dumbledore looked up from the letter he was writing when a golden light filled his office.
He found Fawkes sitting on the carpet in front of his desk and behind him on the floor were two little girls, both asleep. One had clutched a tail feather of the phoenix with her one hand, while holding her sister's hand with the other.

Professor Dumbledore smiled softly and stood up. He approached the twins and bent down slightly to free Fawkes tail. The phoenix looked slightly perplexed since he never had a five-year old grab his tail feathers before. When Professor Dumbledore had carefully pulled Periwinkle's hand away, Fawkes fluttered onto his perch to safety.
Having nothing to hold onto, Periwinkle's subconscious decided that Professor Dumbledore's thumb would be the next perfect teddy substitute.

The headmaster looked down at the sleeping twins and noticed that the scars on their hands looked exactly as they had four years ago. Their black curly hair was obviously something they had inherited from their father, but he knew that their eyes were the same as Lily's. Or similar, at least.

Professor Dumbledore slowly conjured a brown cuddly toy the shape of a cat and swapped it for his thumb. Periwinkle instantly sighed contently and pressed it to her chest.

The headmaster levitated both onto a couch in the corner of his office, making sure to keep them together because they wouldn't let go of each other's hand.

The door to his office slammed open.
"Albus!", Professor McGonagall thundered as she stepped into the room, followed by a scowling Professor Snape. "You would not believe what a Slytherin just did to my Gryffindors-"

Professor Dumbledore held up his hand and motioned them to be silent.
Then he gestured to the couch behind him.

Professor McGonagall looked irritated and moved to the side to see what he was pointing at. Then her eyes widened in surprise.