A short drabble that popped into my head after reading the seventh book. I hope you get it. DH spoilers, so beware.
Always
"It's impossible."
"No it's not!"
"It is! It's beyond O.W.L level, and we're only third-years."
"It's that pessimistic attitude that makes it impossible."
Her eyes, deep green and filled with moonlight and stubbornness, bored into his. He sighed.
"Fine then, prove it."
She jutted her chin forward in acknowledgement of the challenge. "I will."
Her face was a mask of concentration, his of scepticism, as the wand was thrust out like a sparking torch in the black night.
"Expecto patronum!" The words were loud, clear, and filled with fire that dared the world to contradict her. Her eyes were filled with infinite faith and light. His breath was stolen.
A brief moment of anticipated silence, and he could almost see the magical energy flow through her body to the wand, before releasing itself in a silvery white stream of raw power.
It glided serenely over the top of the tower, and he could vaguely make out the shape of a four-legged animal, soft and transparent, before it faded into the night.
She dropped her arm, clearly exhausted. However, her face shone brighter than the patronus as it turned towards him.
"I told you it wasn't impossible. You just need to think of a really happy memory, and concentrate on nothing but the memory." She took a deep breath and straightened. "Now you try."
He eyed his wand doubtfully. "It won't work. I don't have as much power as you." It was true; for years he had been irresistably drawn to the pretty young muggle girl brimming with so much magic.
However, she just gave him small, knowing smile. "It's not about power, Severus. It's about faith."
He couldn't refuse, and tried anyway. But it didn't work, just as he knew it wouldn't. After several more attempts, under her constant urgings, he realised that it was a question of neither power, nor faith. It was about, quite simply, being able to think of something light and pure, and letting it consume the dark, tainted corners of one's mind.
Therefore, his failure to do so did not come as a shock. Completely untainted memories, after all, were all but non-existent to him.
They left the Astronomy tower at around midnight. She offered him a sympathetic smile and encouraged him to keep practising, the faith never once leaving her face. He let her have faith, because someone had to. Someone had to produce a patronus. Someone had to have faith in him.
Snape opens his eyes and releases the river of tears which had built up behind his lashes. They cascade down his face and freeze before they fall to ground; tiny chips of ice that only add to the thin blanket of snow that covers the forest floor.
Impatiently, he swipes a hand over his eyes, and pushes his weight off the tree. He has a job to do and needs the memory, not the tears. True, it is not the happiest memory, but then, not many of his are. The important thing is that it is pure and tainted only with the fact that such a thing will never exist in this world again.
With the image of Lily's eyes burned into the back of his mind like the moon in a dark sky, he points his wand and sounds the words out loud and clear in his mind.
Expecto patronum!
The doe is dazzlingly bright, not in the least transparent. For a moment he just stares, drinking in the sight. Then she turns her head to look at him, and for a spit second he imagines that her eyes flash green before she steps out of the surrounding trees to calmly approach the tent.
The boy follows almost immediately, just as Snape knew he would. He curls his lip slightly into what can almost pass for a smile. Perhaps there is still a little faith that exists in this world, after all.