He'd found the mirror in his second year. At the time, it had been in Dungeon Eight; covered with a musty blanket that revealed only its toes. Had the rat not scurried beneath it, he might never have noticed it - but the rodent, having skidded into the far side of the drape and panicked, began to thrash about with such force that the cloth was dislodged.
The portion revealed was merely a sliver, but in the darkness of the down-below, its radiance was undeniably unnatural. He let the rat go - forgot about it, really - in favour of reaching for the curtain; a black moth drawn in by a silver flame. Dust rose in choking puffs as the cloth, yanked away, collapsed into puddles on the floor; motes that swirled in artificial moonlight, tendrils that writhed around him and stretched toward him. When the clouds cleared, he could see two sets of eyes in the mirror: His own, hollow pools of black, and a pair so vibrantly green and close that their owner must have been right - over - his shoulder. (When had she gotten there? How had she come up so silently that he'd failed to notice?)
He jumped and whirled to face her, lips already shaping in words his head hadn't yet figured out, but the dungeon - and the doorway - were empty. For a long moment, he but stood where he was and stared hard at the shadows, willing them to give up their secrets. When they refused, he turned back to the mirror.
He'd been twelve then, and the visions had been innocent. He knew where babies came from - ("A Muggle book? For heaven's sake." "Well, what do you want to give him, Eileen? Where the Wizard Puts His Wand?") - but the process didn't interest him. When Severus looked into Erised's Eye, it showed him only a boy in black robes and a girl in a flowered dress; his hair clean and hers in pigtails.
He hadn't understood it, and he hadn't thought much of it - in fact, once the rat had reappeared, the mirror had fled his mind as swiftly as the rodent originally had, and he'd gone to finish chasing down his homework (it was Transfiguration, and it hadn't gone well). It wasn't until two weeks later that he recalled what had occurred in the dungeons and resolved to go back for a second look.
That day, the girl in the mirror had reached shyly for his hand. After that, he'd crept down whenever he had the chance - he didn't want to miss classes for it, of course, or risk trying to sneak out of Slytherin after curfew, and he had to make time for Lily - the real Lily - as well. But during lunch and dinner, and sometimes in the afternoons, he could slip away when no one was looking and gaze unmissed into the glass.
When he was thirteen, she kissed him. It started the way it always did - half a sandwich in his hand, which he'd finished somewhere along the way, and a series of furtive glances over his shoulder to ensure that he wasn't being followed. There were still crumbs on his fingers when he reached Dungeon Eight (and what a relief that had been his first day back, to find that it hadn't been moved over the summer), and when the Lily of Erised moved to twine her spindly digits around his, he wiped them self-consciously against his robes as if it was really him she'd be taking hold of. The girl in the mirror laughed, then, and before he knew what was happening, leaned in to find his mouth with her own. Their meeting was quick and clumsy, but Severus would swear later that he'd really been able to feel it. Her. Afterward, his lips tingled.
Somewhere between the end of their third year and the beginning of their fourth, Lily - 'blossomed', her mother had called it; he'd overheard her at the park one day. ("Do you think it's a good idea to let her keep hanging around with that odd little boy, now that she's becoming a woman?" "Oh, don't be silly. They've practically grown up together - he might as well be her own brother. I can't imagine he'd ever think of her that way.") To Severus, who'd witnessed every change as it happened, the outcome of the metamorphosis was nothing special - she was simply Lily, just as she'd always been. To the boys who'd last seen her when her chest was flat and her hips devoid of sway, though, she was suddenly Lily Evans, and would you look at the rack on her? ("Where'd she come from - what do you mean, she's been here for three years already? I've never seen her before in my life!")
That was the year that Potter and Black first put their eyes on her. As she walked through the Entrance Hall, James let out a wolf whistle that made her stiffen, and Sirius - well, it didn't matter what Sirius had said; what mattered was that it turned her crimson and quickened her pace. Severus could have done any number of things in response to the insult - he could have attacked the boys, though he'd never been much of a fighter and they outnumbered him two to one, or he could have jinxed them, or he could have said something insulting right back - but in the end, he settled for glaring pointedly over his shoulder and sliding his arm around Lily's waist before escorting her away. He settled on it for two reasons; one, because he really did want to protect her, and two, because it gave him an excuse to feel her up - no, out. Out. Feel her out.
She didn't shy away from the touch, but neither did she seem particularly interested in encouraging his hands to roam. He was practically her brother; they'd grown up together, and she just didn't think of him like that.
The Lily in the mirror, though - that Lily wore her robes a little tighter, hooked their neck a little lower. That Lily smiled coyly and winked at him, and when the Severus in the mirror put his arm around her, she leaned closer in such a way that the robes slid off her shoulder. It was a white shoulder, smooth and unblemished, and he could follow its line either toward her arm, or in along her neck. If he chose the latter, it took him to the ridge of her collarbone, and her collarbone to the dip of her throat, and the dip of her throat to the soft swell of her breast. When his hands - because it was him in the mirror, wasn't it? And if it was, then they were every bit as much his hands as those that fidgeted in front of him - found their tentative way to her chest, she laughed and laid her own gently beneath his wrists, and when he fumbled with the clasps that held her clothes in place, she showed him how to undo them.
She was naked to the waist, and the unbuttoned portion of her robes fell to hang in soft folds around her hips. He could see to her navel and beyond; even to the subtle shadow behind and just above the cloth. If his eyes travelled down, her hips flared; if they travelled up - and admittedly, there was more to see upward just then - her form curved in until it met her ribs. Above that, it was reshaped further still by the just-budded breasts. Even in their sudden abundance, they were girlish still; fresh, untouched, not yet distorted by time and milk and the suckling mouths of babes. They were as pale as her shoulder - paler, perhaps, for her shoulders had known the summer sun - each tipped with a pink rosette. In later days, more jaded days, he would look back on the memory and realize that her nipples had not been so perfectly round, that one of the mounds was just slightly larger than the other - but at that moment, she was flawless; a marble goddess rising from the midnight sea. Her hair was loose and wild, red ribbons framing her face like a gift meant only for him, and her eyes - god, her eyes. If he lived to be six hundred, he would never forget those eyes. The green of spring; the promise of life.
He might have uttered her name, but her breast was in his mouth. He was fourteen and knew nothing of foreplay; he only knew that he had to taste her - had to take her, to take what she was offering him before she came to her senses and took it away. She would forgive him, anyway; the Lily of the mirror could forgive all sins just as could the Lily of the real world - the Lily who defended Severus as Severus defended her; the Lily who would someday be as real in his arms as this. This Lily tasted much as he imagined that one would; faintly of soap and faintly of perfume. His own skin tasted of salt and the snake scales he'd been scraping for Potions, but hers - hers was clean and sweet. Pure.
The pink nub grew tight and hot under his tongue, and as her fingers crawled to his shoulders, where they curled in and latched on hard, her back arched to lift it all the more. She made no sound - she never did, for some reason; for all the seeming realness of the mirror-dreams, that was one detail they lacked - but her mouth was open in such a way as to suggest that she was gasping, or moaning, or perhaps calling out his name. Somehow, even as his hands were on her waist, they were in his robes; they had hold of his cock, and something warm and wet was dribbling over his digits and to the floor.
The spell was abruptly broken. He stared in disgust at the tiny puddle that had formed beside his shoe - it was on his robes, too, and he could tell that it was going to dry to an all-too-visible white. The Lily of the mirror didn't seem to mind, though; she only smiled and waved as he turned swiftly and slunk away.
He couldn't meet the real Lily's eyes the first time he encountered her in the halls after that - or the second - and even on the third, he was still convinced that the flush of his normally-sallow skin would give it away. Eventually, the shame lessened enough that he could carry on a conversation again. He was doing as much for her as himself, after all; so that when she finally came to him, he'd be ready.
Midway through his fifth year, she let the robes drop all the way. It was well after midnight - he'd given up on trying to make it to and from the dungeons (with a towel in his hands, no less) unnoticed, and besides, everyone was sneaking out those days. Even the self-righteous snots from Gryffindor. Actually, the Gryffindor lot was probably the worst about it - they all believed that no one would ever suspect them of deliberately breaking the rules, and took wild advantage of the fact.
The mere thought of James and his lackeys made Severus grit his teeth and go tense, and the Lily of the mirror noticed that. White willow-branches, her arms draped his neck and her lips turned to brush his ear. They moved with the same silence as ever, but he knew what she was saying: He needed to relax, and she knew just how to help. There were her shoulders, danced over by ringlets as messy as they were artful, and there were her breasts - fuller, now; their nipples more ruddy than baby's-room pink - and there - There was that thatch of curls he'd only ever gotten a glimpse of before, doing as much to reveal what lay behind as they did to conceal it. He understood then what Sirius had meant when he'd once murmured, "Do you suppose the carpet matches the drapes?" as Lily passed by; if Severus had grasped it at the time, he would have given Black an eye to match his name and socked Potter similarly for sniggering in reply. But with the Lily of Erised beside him, guiding his hand between her thighs, it no longer mattered. He knew secrets they would only ever wonder about.
His fingers had become as calloused as they were nimble, the victims of slipping knives and caustic chemicals, and he feared that he might snag her skin on them as a pair of silken stockings might be snagged and so torn - but she had fought him hard to be first in their class, and knew herself what became of an adept potion-maker's hands. Even had she not, she would have forgiven him; she always did, always had. The roughened digits explored gingerly the part of the cleft that crawled onto her torso; parted the delicate folds and dipped down to find what else laid there. When they reached the nub hidden at the apex of her thighs, she shuddered and her hips rocked forward; he wound his other arm around her waist and pulled her in so that her back was against him, and let its hand rise to seize her breast.
There was warmth and wetness between her legs, though the texture of the latter was subtly different from his own emissions; it spread across her labia and matted the scarlet curls. His thumb continued to stroke the swollen bud above, and when she pressed pleadingly down against his hand, he at last allowed the rest of his fingers to curl in and search for the hungry opening that he knew was there - somewhere -
They found his prick easily enough, though, as they always did; tightening, tugging, releasing. When he came this time, it would be into the towel; he would fold it up and secret it away to the laundry inside his sleeve and no one would be the wiser.
Six months later, he called Lily - the real Lily - a Mudblood, and after that, there was no need to worry that he'd be found out anymore. There was nothing he could do that would lower him any further in her eyes; nothing that could cause her to turn away so quickly. So sickly.
He went to the mirror once more before the end of term. In it, Lily was on her knees with her robes askew; her lips parted to speak unheard words. The Severus of Erised had his cock out, and after Lily blessed him with her forgiveness, she would probably bless that by taking it into her mouth.
It was what he wanted; the mirror would never have shown it otherwise. It was also a dream, farther from reality than ever, and it meant nothing. The eyes that had once been so brilliant were lifeless, empty; the silent words so hollow as to echo off themselves, the sex as cheap as what he could have gotten from a Muggle whore. That Lily might have forgiven him - would forgive him, as she inevitably did - but Lily, the real Lily, would not. Always before, he had believed what the mirror had shown - had held out hope for it to reflect in the world beyond - but he knew then that it lied, and the knowledge left a bitter taste in his mouth - something metallic and unclean; something as impure as the blood that ran in them both.
On his way back to the Slytherin dormitories, he stopped to put the towel, still folded, back in the linen room.
In the spring of his sixth year, he raped her.
She had refused to speak to him over the summer, going so far as to get up and leave if she happened to see him headed her way. Eventually, she'd stopped coming to the park altogether. He'd sent owls, and the owls had been sent back with the letters still in their beaks. It was Lily, not pride, that had prevented him from apologizing - and so, it became Lily who was at fault for the rift between them. He had wanted to believe her as pure as any of the old families, only to find her no better than what she was - a child of filthy blood, of Muggle blood.
What did that make him?
He still wanted to believe her pure - perhaps for his sake as much as hers. In the darkest recesses of his mind, he still did. But the rift was a raw wound, and it festered, and when he returned to Hogwart's to see her laughing with the Gryffindor girls and turning her face from him, it was as if salt had been rubbed into it all over again.
When he stood before the mirror, it was night both outside the walls and in the glass, and the green eyes of Erised's Lily were wide with terror.
He was seventeen when he looked into the mirror for the last time. Its silver sky was darkened by the clouds of a coming storm, and the ground below moist with some glistening fluid. He knew the scent it would have had, could he in fact have smelled it; it would have been cloying and metallic. There was a figure at his feet - a man, half-stripped and still, his skin rent by countless seeping gashes - and at his side, there was Lily; blood staining the hem of her white robes. Her eyes were greener than he'd ever seen them: Vivid and vicious; so intense they seemed to belong to something that was not human. Beautiful and monstrous all at once; a Lily who delighted in the jealousy she roused in Severus and who reflected it right back at him. The Lily that could have been, should have been; a Lily who would have remained offended by Potter's advances and continued to reject them.
He groaned and half-bowed his head, letting it rest against the mirror as he fumbled to find the opening in his robes. His shaft was already engorged and aching, and when his fingers brushed it, it leapt as if touched by Lily herself. He lifted his eyes, intending to steal another glance at the woman who had loved him, denied him, tormented him -
There were three pairs of eyes in the glass, and the third - as blue as a summer sky - overlaid Lily's in a way that they could not had they been part of the scene themselves.
"I think," Dumbledore said quietly, "that it may be time to move the mirror, before another soul is lost to it."
Severus said nothing for a time. Bitterness warred with self-preservation; one wheedling with him to snap back that he was already lost and had been for some time, the other prompting him to hold his tongue. In the end, it was shame that won out; he only nodded numbly and pushed away from the mirror, withdrawing his hand as surreptitiously as possible from his robes.
In the doorway, he paused to gaze a final time into Erised's Eye. The glass, though it gleamed with the same silver sheen he'd seen from under the curtain that first night, was empty, and he found himself wondering if it had always been so. Lily was not there, certainly; or at least, not his Lily.
His forearm itched, and he reached absently into his sleeve to scratch it. There was a siren's whisper in his head; the call he'd never been able to hear in the mirror.
It was time to answer it.