DISCLAIMER: Everything belongs to JK Rowling. This humble first attempt at HP fanfiction stems from a wish to play in her universe for a few borrowed moments. Please don't sue.
His light footfalls were barely discernible upon the corridor's cold stone floor. Billowing, black robes followed the wake of his long, agile strides as he stalked through the familiar old staircases and hallways.
It was just another day. Another year. And for Severus Snape, this only meant that another bunch of open-mouthed dunderheads was being unloaded on school grounds by the boatfull at this very moment. He continued his silent trek towards the Great Hall. Countless times he had roamed the bowels of the castle in his youth. Little did he know then that he would long remain within its walls even as a man: a willing prisoner amongst these same walls he both loathed and loved with equal passion.
The first few years back had been true torment. Castle walls and chambers stood as silent witnesses of what had been his life and what was now left of it. Fleeting glimpses from years past perpetually haunt his mind's eye, both balm and dagger to a heart past all mending. But it was simply not in his nature to take a beating without putting up a fight. And so he did what he did best. He did what had ensured his survival through a myriad of bludgeoning fate had been dealing him since he was but a mere boy. He put up walls. He built a fortress around his frayed soul, resolving never to let anyone in ever again.
This was how he lived. This was how he planned to stay alive to see through to the final purpose he had left -- the sole purpose that kept him breathing.
He was an efficient teacher, the youngest by far among the staff. His keen, penetrating mind and singular skill rendered him more than qualified for the position. And even yet as he taught the subject he excelled at the most, he knew no joy, no satisfaction.
He was exacting. He allowed no ounce of leniency and had all but set his expectations in stone. Infamous for his acerbic wit and barbed words, students quickly learned to stay away from his path. He withdrew from all human interaction and channeled all his energies into fulfilling his duties: no more, no less.
The excited hum of children assaulted his senses as he reached his destination. He unceremoniously claimed his place at the staff table, the way he did for the last ten years. Students unfortunate enough to accidentally meet his steely gaze quickly looked in another direction. He was dimly reminded of ancient Muggle emperors whose subjects averted their eyes as an act of reverence. "Emperor indeed. And of what empire?", he sneered to himself savagely.
And it was at that inauspicious moment, following a chain of unremarkable events that spanned a decade, in a sea of forgettable faces, a startling pair of green eyes sent a sudden jolt to his consciousness.
Eyes he thought he would never see again.
And in his gut he knew that from this year onwards, nothing would ever be the same.