This is what happens when I'm bored in France with too many feels... It hasn't been beta'd or anything so sorry for mistakes.
In a damp, dark, cold cell deep in the midst of Azkaban prison a man lay on the stone floor. Outside, dementors swept soundlessly past the bars and in the distance, a woman screamed for help. The man sat up, trying to look through the clouds and mist to see the moon was hopeless. How long had it been since he'd seen the moon? His eyes flicked to the wall with the scratches that started counting days but drifted into just months, finally stopping altogether. It must be nearly a year now. Maybe two.
Letting out an anguished sigh he stood, walking to his bars with the movements of somebody twice his age. He grasped two of the thin metal poles and pulled himself up to stand straight. One dementor pulled away from the rest to glide down to the man. His hooded figure with its face level with the prisoner's. Anybody else would have thrown himself against the back of their cell in fear but Sirius Black stood his ground. He didn't care about the soul sucking monsters. His soul was broken already. Eventually the dementor got bored and drifted off to the cell next door, which, as it happened, contained his cousin. Bellatrix Le Strange. He thought back to her in school, with her wild black hair and dark eyes, scoffing at him and gliding elegantly off with her sister. What a difference to now, the thin arms he occasionally saw reaching between her bars were a shadow of what they were then, almost skeletal and just as white as bones.
Looking at his own arms he sucked in a quick breath. Where his arms used to be muscular and strong they were now skinny and held the slightest memory of muscles. On good days he would do press-ups, but they didn't come very often anymore. Scars ran up and down, covering him from shoulder, to elbow and even down to his wrist. Scars from years of abuse from his parents, scars from Quiddtich, scars from play fights with James- even thinking the name sent a jab of pain to his broken heart. Finally there was his tattoo. The dark outline of a moon which changed in synch with the lunar cycle. Today, his tattoo showed a full moon.
The tattoo was how Sirius had counted the passing months when he first came to Azkaban. But when he'd got the tattoo, he'd used it for something very different. One of his best friend's- well, his boyfriend. Was a werewolf. The tattoo helped him know when 'moon week' was coming up, when he'd have to be extra loving. Mr Remus Lupin. Thinking of him hurt more than thinking of James. Remus had to live everyday thinking that Sirius had betrayed them. That Sirius was the reason James and Lily had died. He pushed the thoughts from his mind, in the first few weeks the thought of Moony hating him made him scream louder than the dementor's kiss. Sirius tried to think back to earlier times, in Hogwarts. In third year him, James and Peter- the bastard- had become animagi. They used their animagus forms to keep the werewolf company on the night of the full moon. In a sick way, it made up some of Sirius' happiest memories. He used to hate that he got fun out of Remus' condition, but Remus claimed to enjoy it as well 'The pain of the transformation is lessened by the fun we have as animals' he used to say.
Sirius hadn't realised it but he had been stumbling backwards in the dark. He now hit the far wall, his knees giving out. Tumbling to the floor with a dull thud he was reminded of when he'd been to the Lupin house for the first time. Remus had shown him the shed where his parents had been forced to lock him in during every full moon. There were deep scratches covering the walls, door, floor and even some on the ceiling. Blood stained the wood a deep red. Remus told him that he'd never been back to the shed, not since his last full moon at home, it contained too many bad memories. He looked so vulnerable, all Sirius could do was hold him close and swear, promise that Remus would never spend a full moon alone again. He'd kept that promise for years, until that night when he went out to stop Peter, and ended up getting framed himself. Being in Azkaban meant he had to break his promise. Remus was alone.
Everyday his brain found a way to remind him of that, and everyday it hurt. But on the night of the full moon it was ten thousand times worse. He could only imagine the pain Remus felt, but he knew that it hurt much, much more when he was alone. Sirius' only way of consoling himself was to tell himself that they'd found a cure. That Remus never had to face the pain alone again. That moon week was just another week to him, and the full moon held only memories. He always knew he was lying to himself, that it wasn't possible, but it helped all the same.
The night of the full moon would come to pass, but for the rest of the night Sirius paced. He couldn't sleep, occasionally he would stop to sit or lay down for a while, but if he did that he started to think, and that wasn't good. Pacing took his mind off of everything. He counted the amount of steps he had to take to walk around the room; he created shapes on the floor. Finally his tattoo would shift, the night would be over and the ache in his heart would lift just enough to let him sleep. And when he did, two words span around in his head 'I'm sorry.' He was sorry that he wasn't there, sorry that he hadn't told Remus what he was doing before he'd left on that night, sorry that he'd never be the Godfather he'd promised to be to James's son Harry, he was sorry he would never get a chance to put any of it right.
Ten years later, on the night of the full moon, Sirius Black escaped from Azkaban prison. He had promises to fulfil.