One month after it happened, Xander Harris had already started becoming used to being a woman.
Well, 'used to' in the sense that he didn't wake up and start screaming when he discovered he was lying on his breasts, and that he was tolerating having to sit down to pee, and everything else that had happened.
It wasn't a complete change; he hadn't gotten his period. Which was the only saving grace of the situation. The only one.
Anya had declared herself uninterested in women – or maybe it was just that she was jealous that Xander as a girl was prettier (and chestier) than her – and broken off their engagement.
Two months after it happened, Xander had moved into Giles' house with him and Spike. His parents hadn't taken it well, finding out that their son was now their daughter. Thankfully, the construction company he worked for was willing to hire 'Alexander's cousin Alexandra' on a trial basis to fill in for him while he was in the hospital recovering from a car crash. 'Xandra' couldn't lift as much as he used to, but all the knowledge was still there.
It was only a matter of time before he received all of it.
Recovering his proper body was looking less and less likely.
Five months after it happened, Anya went back to being a Vengeance Demon. Xandra couldn't talk her back to the side of the light, but she did at least leave Sunnydale before doing anymore damage than the slaughter of the fraternity.
Six months after it happened, Xandra and Willow got drunk on the anniversary of Jesse's death. They talked about their past loves and losses, Xandra crying over Anya and Willow sniffling over Tara. While consoling each other, they accidentally kissed. Less accidentally and more on purpose.
Thankfully, Tara didn't walk in on them, but neither of them acted the same around each other after that.
Seven months after it happened, the Potentials had been activated. None of them were aware of Xandra having ever been Xander, or being a guy. Xandra wasn't sure how to feel about that.
But since it looked like she might never become a he again… Well, it wasn't the end of the world. And even if he had no one in his life, Willow was happy once again with Tara.
Eight months after it happened, Warren Meers went on a rampage and Tara was killed. Xandra had to talk Willow down from ending the world, which he never ever wanted to have to do again.
He couldn't lose Willow. After everything that had happened…well, Willow was his world.
Nine months after it happened, they fought their final battle with the First Evil. Xandra almost lost her eye – would have, if she'd been as tall as he had been – and Robin Wood got seriously injured in their retreat from town. The Hellmouth imploded and took Sunnydale with it. Xandra and Willow celebrated with yet another near-death kiss, this time one that was after the fact and more of a celebration.
On the bright side, Xandra realized that while Willow would always love him, sex was more possible now that he was a woman, too, even if he did sometimes doubt the veracity of her 'Gay now' claim.
One year after it happened, the remaining Scoobies and a slew and a half of Slayers helped Angel Investigations, now Wolfram & Hart, defeat the Circle of the Black Thorn. It was only another army of demons. And a dragon.
It was the dragon that really stuck in Xandra's mind. She also wasn't getting over Wesley flirting with her anytime soon. Even after he found out that Xandra used to be Xander, it didn't put him off for long. Xandra blamed it on post-battle adrenaline, and the realization that they were all still alive.
Well, except for a few of the baby Slayers, may they rest in peace.
Willow blamed it on Xandra's 'great rack' and 'extreme sexiness.' Xandra declined to argue when Willow started doing that thing with her tongue.
Five years after it happened, gay marriage was finally legalized, and Xandra and Willow tied the knot in L.A., with Lorne, a certified judge courtesy of the remnants of Wolfram & Hart being turned to good by Angel, officiating.
Clem was the only one who cried. Or at least that was what the six months pregnant Cordelia made them all swear to.
Forty-seven years after it happened, Xandra Rosenberg lay on her death bed, surrounded by her family and friends. She knew Willow wouldn't have as hard a time dealing with her death as she did Tara's; they had their kids (adopted, of course), their nieces and nephews (courtesy of Dawn and Andrew, Fred and Gunn, Faith and Robin, and Cordelia and Wesley), and all the not-so-new-anymore Slayers.
They'd had forty-six years of happiness together, but it had only taken one for Xandra to realize that she was glad it had happened to her.