Disclaimer: I don't own Buffy, Supernatural, Charmed, or Fable. These belong to their rightful creators.
Prologue
The Hero King of Albion stood with his sister, his faithful dog, and his fellow Heroes while looking down at his second set of Twins in the arms of his Queen. Next to his wife's bed were his eldest twins, Princess Faith and her brother Prince Logan.
Faith looked up at her father asking, "Daddy, what are their names?"
Hanna agree, "Yeah Your Majesty, what are you going to call the little ones?"
Sparrow grinned at the former Hero of Strength before answering both questions with, "Well Faith, you littlest brother's name is Andrew and your little sister's name is Lillian."
Reaver spoke, "Well your Majesty as fun as this has been, I must be going." The others agree and bid the King goodnight before letting themselves out of the castle. After everyone was gone Sparrow took his two eldest back to their bed chambers to rest.
That night one of the Senior Partners swept into the nursery and took the baby boy from his crib before grabbing the little girl from her room.
It's been twenty years since that day as both unknown Prince and Princess stood on the edge of the town formerly known as Sunnydale. Faith stood watching all the Scoobies bask in the knowledge that they won, they closed the Hellmouth forever.
Andrew was standing by the bus and was watching the Dark Slayer as she stood at the edge of the close knit band of heroes known as the Scooby Gang. The young blonde man couldn't shake the feeling of familiarity whenever he looked at the dark haired Slayer's aura.
After about ten minutes the survivors all headed to LA and the Fang Gang. Andrew and Faith hung around for about a month before the blonde boy got the feeling to roam. As Faith was waiting for her name to be cleared, she couldn't help but think the wonders of Angel running Wolfram & Hart. Faith was given a '67 Dodge Viper from Angel while Andrew was given a '69 Ford Mustang.
Two months after Sunnydale fell Andrew was in a small café just off the campus of Stanford, he was there tracking down a newly called slayer. He and Faith had split ways just after they left LA. The blonde boy got up from his seat with his head still in his papers and headed to the door. Just as he was about to exit another young man who's nose was in his textbook slammed into the former Sunnydaler. Andrew's coffee cup lid popped off as it fell to the ground and the drink splashed both men as they both dropped their papers and books.
Sam Winchester had just entered his favourite off campus café when he bumped into another guy and the young Winchester watched as coffee covered his pants and his text book while it covered the other guy's pants and papers.
Andrew groaned, "I'm so sorry."
Sam replied, "It's okay."
"I'm Andrew."
"Sam"
With that the two ended up picking up their stuff and found a table, after sitting down the two started to get to know one another; Andrew found himself quite attracted to the taller man before him, while Sam was kind of shocked that he was attracted to another guy, period.
It had been four months since Faith was cleared and left LA, she knew that her younger friend Andrew was settling down from the wonder lust somewhere near Stanford but Faith herself found her way to San Francisco. While exploring the City by the Bay, Faith found out that there was a great club called P3. The woman who suggested it was a hottie make no mistake but Faith found out that the woman was related to the owner somehow.
Paige was walking on the pier noticed a gorgeous dark hair woman just basking in the evening light, Paige walked up to her when the woman asked, "You know any good clubs around here?"
The youngest Halliwell replied, "Yeah, P3 is pretty awesome." After Paige gave the brunette the address she had to leave to keep from jumping the other woman, she had never been that affected by a person, same gender or otherwise, as she was by the dark haired woman.
Upon entering the club, Faith found it to be quaint and kind of like the Bronze in Sunnydale. The Dark Slayer looked around the room and noticed the woman from a couple of hours earlier, walking up behind the woman she tapped the auburn haired woman's shoulder asking, "Want to dance?"
Paige was by the bar chatting with her eldest sister Piper when a slightly familiar husky voice sounded from behind her, turning around she found out that it was the woman from the pier that was behind her, Paige glanced over her shoulder at Piper before replying, "Okay."
Piper watched as her little sister went out on the dance floor with the woman, she didn't know that her sister was interested in the same sex but even she couldn't deny the sparks that flew in just ten seconds between the two.
Phoebe was on the other side of the room when her empathy sensed a change in her younger sister and she picked up on an attraction that Paige was starting to feel, the Middle Halliwell looked around and found her sister dancing with a brunette about her sister's age but both women on the dance floor seemed to be fighting the attraction.
Just then a band of demons attacked, Piper put the whole club into stasis but was shocked when the woman dancing with Paige just reacted by fighting the demons, Faith for the time being decided to shrug off the not moving dancers and slay the demons likes she's used to. The dark Slayer noticed that her dance partner and two other women were working the mojo and just as they released it Faith jumped out of the way.
The four talked as the Halliwell's learned about Slayer's and Faith learned about the Charmed Ones. She was given room and board at the Manor as long as she wanted, Faith took them up on their offer because she wanted to get closer to the youngest Halliwell.
A couple of weeks later Faith decided to drop in on her best buddy, so she asked Paige if she would orb them to Andrew. When the two women got there they saw a sweaty Andrew with some guy and both were naked and they looked like they were just about to start round two when Faith and Paige popped in.
Andrew yelped, "Shit! Faith, what are you doing here?"
Faith grinned, "Well first, get some Andy-boy. And second, I was coming to see my little buddy."
The two women left the room to let the men get dressed. As Sam came out Faith pulled him to the side and gave him a quick but clear warning, "Hurt him, you die."
The four talked and ended up living together until it was a month before the anniversary of the fall of Sunnydale. In that month both Andrew and Faith were called to Cleveland to help get ready for the apocalypse that was coming that spring.
While in Cleveland Willow was doing a spell to find some of the mini-slayer's family, when she accidentally uttered the wrong names. As Faith and Andrew entered the research room with their mates Willow's spell hit the two full speed.
Faith started, "What the Hell? What was that!"
Willow said, "A family finding spell."
Andrew spoke, "Then why are Faith and I glowing?"
"It means you two are family like blood related. The color you're glowing means your siblings."
The Scooby gang left the other four alone when suddenly an old woman appeared in front of the two newly named siblings. The woman spoke, "My name is Therasa. And it is time for you two to go home and claim your rightful place in Albion."
Faith looked the woman up and down before saying, "Lady, what are you talking about?"
"Have you ever felt like you didn't belong here?" At the two's nod she continued, "Twenty years ago two children were stolen from the beds from the Palace of Albion, their father was the Hero King. Some beast came in the middle of the night taking a three year old girl and an infant boy. Now these two children alongside their mates must return and bring order to the chaos."
Paige spoke gently, "I can't go. The Power of Three would be broken if I did."
"It would not for an older sibling shall be brought back. You, young one, are needed by your mate or all of Albion shall fall to Darkness."
The four agreed to go after Paige had Prue brought back to take their sisters' a note from her explaining what was going on. Therasa opened a portal to the Spire as Faith, Andrew, Sam and Paige walked through.