Longing
Sirius Black moved restlessly about his cell in Azkaban. It was small, only a few feet in any direction. He walked from one end to the other, furrowing his brow in deep thought, though not many thoughts would hold in Azkaban. There was something different about this day, something special, but he couldn't recall what. There was so much he couldn't remember anymore, and it scared him. When he transformed himself into Padfoot, though, the memories and thoughts were stronger. The Dementors didn't seem to notice when he became a dog. He tried to stay in dog-form for as long as possible in order to think of better times.
As Sirius looked out the tiny slit of the only window in his cell, he saw the moon gleaming brightly. He tried to stick his hand out the window to feel the frigid air whipping against his skin, but it was too narrow. The air inside his cell was always cold, but it never moved. Outside the air moved, like a living being; inside, it was stagnant, dead. He did the only other thing he could instead: he put his ear to the slit and listened to the waves crashing in the ocean below. He longed to be out, all the time, but the longing was particularly bad right now.
He closed his eyes and sighed before transforming himself into Padfoot. Within minutes of his change, he remembered what was different about the day. It was Christmas Eve. His first in Azkaban. His first since James and Lily…It was hardly a fun milestone. Even worse torture than being inside the prison was not knowing where Harry was or who was caring for him. Was he happy? Was he safe? He was too young to understand anything that had happened to his parents, and as his godfather, Sirius should be there for the child. But he was here instead.
Padfoot's mind flashed onto fleeting moments of Sirius's past. Christmastime at Hogwarts when he'd been a student. Christmas with James's family. Even Christmas with his own family would be preferable to this. Nothing said "holiday cheer" quite like watching a man receive a Dementor's Kiss. It was definitely one reason to be glad there wasn't any mistletoe around.
Padfoot's thoughts turned from memories, to thoughts of the present time. He should be with Harry, helping him snap his Christmas cracker and placing the tissue paper crown on his little head. He'd make sure it was a gold or crimson crown. He'd read the joke to Harry, and help him play with the toy that would be inside the cracker. He should be with him, holding the little boy up as he put the star on top of the Christmas tree. They should be throwing tinsel on the branches, and hanging up brightly coloured ornaments. Who would help Harry open up his presents? And who would help him play with them? He'd have gotten Harry a set of magically flying motorbike toys, and they could have played with them together.
If he could be with Harry this Christmas, he'd have cooked a goose just for the two of them, and would even have attempted to steam a pudding. It would probably have turned out to be a disaster, and they would have ended up eating in a restaurant, but he still would have tried.
He wanted to play in the snow with Harry and show him how to form the perfect snowball. He wanted read to him The Night Before Christmas. And for himself, he wanted to kiss a beautiful woman under the mistletoe. He wanted to sit by a fireplace with a nice mug of hot Firewhisky and listen to the flames crackle and feel grateful for being so warm. But he couldn't. Instead, he was here, in a dark, cold prison, in the form of a big black dog, alone.
Padfoot drifted off to sleep soon after that, the moonlight gleaming down on him from his window. He dreamed of a Christmas tree with presents on the branches, and a hot, golden roast goose on a table heavily laden with other delicious foods. They were the sweetest dreams, and when he awoke, he wanted to revel in them, but he could hear a guard coming with his food for the day. He tried his best to keep the memories and thoughts within him, but when he transformed back into Sirius, they were gone, and all he knew was the darkness of his cell.