As Professor Dumbledore had once said, young Harry Potter, like hundreds before him, had discovered the delights of the Mirror of Erised. And as it so happened, one Sirius Black, like hundreds of others before him, or maybe many more, had never known about the Mirror. He did not have the slightest idea that such a thing existed. Among the few secrets belonging to the Hogwarts castle that the Marauders had never unravelled, this was one.
It's curious how Fate likes her yarns to fall in such strange patterns.
Had he done so, Mr Black would have seen things which would have made his heart beat at the double. After suffering years of injustice, betrayal and loss, he would have looked at the heavy golden frame with the inscription — Erised stra ehru oyt ube cafru oyt on wohsi, with wide eyes. Those words might have made sense to him, or perhaps not, but it wouldn't have mattered, because the things that the age-old glass showed him would capture all his attention. He would see the very picturisation of the deepest of his desires, which had gnawed at him all those days in Azkaban, eating him alive, making him feel worse than dead.
The mirror would show him the ever so familiar house decorated for Christmas — a large tree at one corner decked with all kinds of bits and fancies lighting it up. The Potters' cottage at Godric's Hollow always looked more welcome than ever at this time of the year. He would see his best friend, or brother, as he had always considered James so, standing in the hall hanging a sprig of mistletoe, youth lighting up every one of his messily handsome features, his glasses a little lopsided as they always were. Lily would come up from behind and wrap her arms round him, laughter beautifying her already gorgeous features. James' hazel eyes would sparkle in delight, and abandoning his work, he would sweep his wife up and kiss her, swinging her around. The couple would break apart at the sight of their one year old son, who would tumble over to them with silent squeals of joy. The family would look perfect, without any trace of worry or distress upon their features. That was how things were supposed to be.
Sirius would watch hungrily, his haunted gray eyes lit up with those long lost memories, as the glass showed him the scene — a gateway to another dimension, he would feel. A place where things are better, where things are right.
The scene would continue to unfold, as another individual joined the little family. Remus Lupin would walk in, his clothes nice and warm, and obviously well-tailored, his hair devoid of its limpness and in all its caramel splendour, not a single scar marring his face or hands. He would smile at his best friend and take little Harry up in his arms. The toddler would giggle and pull at his hair. Remus would say something, and although the mirror allowed no sound to pass through, Sirius could decipher it as "Merry Christmas". The house would be bright and lovely; a very merry Christmas indeed.
The group would make their way to the dining room, where dinner would be laid, all set to be eaten. Lily had always been an expert cook; the turkey looked very inviting.
It would be here that Sirius' eyes would fall on another person who stood lazing against one of the chairs, who would straighten up with a huge smile at the sight of his best friends. Dark hair falling into the eyes with a unique casual elegance which time would erode, muscles showing against the jacket which would later be reduced to mere skin and bones, and gray eyes full of laughter, which would, years later, grow dark and fathomless with the harshness of cruel circumstance — that figure, ever so familiar.
Sirius would lift his hands to touch the cool glass of the Mirror even as his twenty-one years old self reflected his action, his burning gaze full of desire clashing with the mirthful one of his younger counterpart. Minutes later, the young man would turn away to join the celebration at Lily's call, the little family gathering round the table, identical smiles brimful of joy on their lips, without a care in the world.
What the Mirror showed was a dream, a refined version of the memories that Sirius had cherished — a world untouched by war, pain or prejudice, where everything was perfect, where those he loved where happy, where Youth and Laughter ruled the world. A world so different from the debris that made up his own; a world so far from reality, and yet so easily what it could have been, had a few things not gone the way they had.
Sirius would watch, tears rolling down his eyes, as his desires found an image, transfixed, willing the glass to absorb him, to take him through. At that moment, he would forget everything except that beautiful mirage, and would let it absorb his heart and soul. Reality and dreams would no longer have separate boundaries, all a whirl of colours and pictures. For hours and hours he would stand still, watching in fascination as his friends, his family, waved at him, as James and Remus mouthed words of encouragement to him, as Lily blew him kisses and little Harry waved at him with his chubby fists, and his own younger self wrapped his arms around them all protectively, and offered a little nod — a silent promise that he would never let them go. Sirius would watch until his brain finally gave an alert of time, and then with a regretful smile he would wave at them and leave. And every day he would come back to the Mirror and see his dreams played out on the strange glass, watch James and Lily smile and laugh and wave at him, and he would let the Mirror of desire own his heart and soul, and completely lose himself in the life that did not exist.
But of course, Sirius Black had never had the opportunity to get acquainted with the Mirror of Erised in his lifetime, and let us just say that it may or may not be beneficial for his sanity and happiness (but the two do not essentially coexist, do they?).