They hadn't meant for it to happen, it just did. They awoke in each other's arms, their lips only centimeters apart. Their naked bodies were intertwined.
Xander was the first to wake.
He saw a face and peroxide blonde hair. He screamed. He felt Spike's leg rubbing his own, it felt strangely pleasurable. It also felt nude. Xander peered under the sheets. He screamed once more. This time, the sleeping vamp awoke.
"Morning love, what's the matter?" Xander jumped out of the bed.
"What's going on?" he asked, struggling to put his pants on.
Spike got out of the bed and in all his naked glory, walked over to Xander. He enveloped the scared brunette in a warm hug and began sucking on his neck. Xander fought the urge to moan. Spike began to fondle Xander's breasts. 'Wait, breasts?' thought Xander. He looked down. He saw two rather large breasts sticking out of his normally flat and mannish chest.
Xander was suddenly bombarded by memories of the past few days; a miscast spell, his transformation, shopping, getting together with Spike, getting engaged. Xander looked at his left hand. A silver engagement ring stared back at him, the sapphire in its center mocking him. 'How did this happen?'
"Come back top bed pet," cooed Spike, "And take off those pants, it'll be hard to enjoy my fiancée the ways I want to if she's wearing clothes." Xander felt Spike begin to unzip her pants whilst kissing her neck. Xander felt her pants fall to the floor.
'This feels, so wrong,' she thought, 'And yet, so right.'
"This spell was the best thing that's ever happened to me," said Spike, pulling Xander onto the bed, straddling her. Xander surveyed the man on top of her. He was a vampire, a vampire that she'd hated for years and yet had feelings for. And now that she was no longer a he, it didn't seem wrong. It felt right, laying under the blonde vamp. She felt safe, complete. She wrapped her arms around his neck and pulled him in to a passionate kiss.
'His lips are so warm,' thought Xander, 'Almost like he's actually alive.' It started with the kiss, which slowly led to Spike's member pulsating with desire. Xander flipped Spike onto his back and began kissing his chest, trailing down his stomach towards his genitals. Xander began to lick Spike's hard, long penis. Her lips seemed to move on their own as she began to suck the head of it. Spike moaned in ecstasy. A growl escaped his lips. He leaned forwards and kissed Xander's neck, slowly lifting her mouth away from his penis. He raised Xander's lips to meet his own in a rough, demanding kiss. His tongue licked her bottom lip, slowly finding its way into her mouth. Xander felt Spike's cool tongue slip inside her mouth and found herself lost in the passion of the kiss.
After a minute, she broke the kiss. She stroked her fiance's face.
"What'll happen if they find a spell to reverse this?" asked Xander. Spike took Xander into his arms and held her tightly.
"As if I'll let them take you away from me love," he said, kissing her forehead.
'I hope not,' thought Xander, 'I never want this to end.'
My first, and hopefully only attempt at a Xander/Spike slash, and just slash in general. Don't flame me.