One stupid mission and Severus Douglas Snape's life as he knew it was over. No, not that mission. During The Dark Lord's second reign of terror there was very little information to be had on the Order of the Phoenix, and his Death Eaters were assigned to find out anything they could, using whatever means necessary. Snape's assignment was particularly heinous. Snape had thought The Dark Lord had borne no ill will for what appeared to be thirteen years of abandonment, but then why this particular mission? Being ordered to seduce Remus Lupin was just the sort of thing to be suspected of the cruelest and most evil wizard of the time.
It certainly wasn't easy. Tracking Lupin's location was nigh impossible, but luckily an Imperiused Mundungus Fletcher proved useful. Then obtaining some hair from Nymphadora Tonks through a contact at the Ministry had caused a black eye and a sexual harassment complaint. But Snape was nothing if not a skilled Potions Master, and the rest of the plan went swimmingly.
He'd only had to stalk out at Grimmauld Place for a week before Lupin showed up (Tonks was reportedly out of the country on Auror business) and Snape made his move while wearing Tonks' face. A quick lie about returning early, a few shots of firewhiskey, a few swigs of Polyjuice Potion every hour and a half, and a couple of very dirty jokes was all it took to get Lupin into bed. Snape had thought that this part of the seduction would be the most difficult, the actual physical connection with someone who had been party to his torment in school, but Snape found that the level of control he had over Lupin in this position to be almost intoxicating. True, it would have been more satisfying with James Potter or Sirius Black (though Snape had already gotten the ultimate revenge upon them), Lupin was long due for his comeuppance (even if he never knew it). Such was Snape's enjoyment of the revenge fucking (as it were) he almost let an entire two hours slide by without a drink of the Polyjuice Potion while he was still tangled in the throes of passion with one of the people he hated most (two if he included himself). Luckily, as amazing a lover as Lupin proved to be (Snape was not one for smoking but damn if he didn't need a cigarette after) he didn't last more two hours and Snape was able to rush to the bathroom before Tonks' nose developed his signature hook and her hair saturated itself with grease.
And even though the pillow talk proved almost useless for intel purposes, this was still not the life changing aspect of Snape's mission.
No, that came two months later when Snape realized that his robes were getting tighter around the midriff and his nipples felt…sore. Though uncomfortable and slightly inconvenient (getting his flowy black robes tailored wasn't cheap), it wasn't until the unstoppable nausea throughout the day came that Snape put together the pieces. Some frantic research in the Restricted Section of the Hogwarts Library proved that a pregnancy conceived on Polyjuice Potion was rare, but still possible, especially when the sperm came from a particularly virile donor (Lupin's lycanthropy seemed to strengthen his swimmers as well as his body). Snape was in a bind. Fetus Deletus was the wizarding version of a coat hanger abortion, and at any rate, Snape wasn't sure the spell would work on a male physiology (even if a uterus had been retained after use of Polyjuice Potion). Snape had only one choice. He would have to give birth to Lupin's baby.
The next seven months were torturous. After the sixth month when he was simply too rotund to go unnoticed, Snape informed Dumbledore that he caught a rare and highly contagious wizarding disease and would need three months of recovery. The same lie was given to The Dark Lord, though with slightly more suspicion, but the promise that Snape would continue to do Death Eatery things from home (after all, someone has to organize all the terrorism) sated him and his followers.
When the time came round for the baby to come, Snape was ready. He had read as much on the arts of midwifery as he could and had found a muggle orphanage of decent standing that would take the child (though he had claimed the child would be coming from a niece, not himself). Snape used some of the leftover Polyjuice Potion to give him a female physique (after all, he wasn't going to push a nine pound baby out of his dick) and steadied himself as the contractions came and went. And then suddenly, his water broke and everything hurt (almost worse than the Cruciatus Curse) and an hour and much labor (so that's why it's called that, thought Snape) later, a squalling lump of human came out of him to join the world. And damn if she wasn't beautiful (at least to him, anyways. Truly, all babies are a sort of ugly only a mother can love). Lily, he named her, though she looked nothing like Lily Potter had and definitely had Snape's own nose and Lupin's tufty toffee colored hair lightly covering her scalp.
Handing her over to the orphanage was the second hardest thing he had ever done, and certainly his biggest regret. He continued to see her at a distance when he could between missions for The Dark Lord or for The Order, and his body would ache with the memory of carrying her and birthing her. After all, he would always love Lily. Always.