Disclaimer: Buffy the Vampire Slayer and Lord of the Rings belong to their respective creators, Joss Whedon and J.R.R. Tolkien.
Author's Warning: major AU. Absolutely non-canon.
Buttercup didn't know how old she really was. She couldn't remember her real birthday, or even the age at which they'd taken her out of the river, her fingers digging into black hair and russet shirt.
Daddy had said she looked about six, and most everyone had agreed, even if some said she was a bit small for six years. He'd asked her then what she'd like her birthday to be, at least until she remembered it, and she'd asked him back what Frodo's birthday had been. Daddy's smile had faltered, his eyes had grown sad, but he'd answered, September 22, and she'd answered back, Mine, too.
She counted it, September 22, every year since Frodo had drowned and she had forgotten everything.
Bilbo's birthday was also September 22. When he found out that they both celebrated the same day, he suggested that she come to live with him so that they could observe her fifteenth and his ninety-ninth together.
“Buttercup, my girl,” he said to her, “it is only sense. It would be easier for us to celebrate under one roof, and then our friends wouldn't have to choose between us every year.”
Buttercup was paralyzed with indecision. She haunted the woods for days, thinking, trying to figure out how to keep from hurting anyone she loved.
It was Mommy who told her to go.
“You spend more time over there than you do at the Hall, Buttercup,” she said gently. “Daddy and I will always be here for you, but if you'd like to try living in Hobbiton for a while, you should. Only visit often.”
Buttercup went out into the woods, the dogs barking beside her, and thought.
She thought about how strained Esmerelda's smiles had become, how worried she looked when Meriadoc asked to go along with Buttercup when she went roving, when he practiced with his sling to be just as good as Buttercup, when he said things like how he wanted to be a hunter when he got older, like Buttercup.
She thought about how the other grown-ups, Asphodel in particular, had been in and out of Mommy's sitting room, her face full of worry as she whispered about how bold and exploratory her own children had become.
She thought about Merimac, and how, though he was Daddy's own son and a great woodsman and hunter, he was still only a second son, taking the second place at the table, with less to his name and his rights than Saradoc.
She thought about how other people looked at her sometimes, the neighbors in the Shire and in Buckland, when they saw her coming out of the woods or walking down the road, her dress dirtied and worn at the hem from where she'd gone through the trees and the fields.
She thought about Bilbo, and all the stories he told, of Dwarves and Elves and Men, of Trolls and Goblins and Dragons, and the sword he'd shown her once, which he named Sting, and all the things he knew about the world outside the Shire that no one else did.
She thought about how, if she stayed at Brandy Hall, she would eventually be expected to marry, someday, to get a husband and be a respectable hobbit, as a foster of the Master of Buckland. She thought about what, exactly, it was that Mommy was trying to do for Buttercup when she told her it was all right to go.
She thought, for the first time, about what it meant to be free and obligated to nobody.
The day Buttercup left Brandy Hall, Meriadoc threw his first tantrum. He clung to her arm and leg and howled when Esmerelda tried to pull him from her, shouting red-faced that he would not live apart from Buttercup. Mommy and Esmerelda tried to calm him, telling him that she'd be by often and they weren't so far from each other at all. He hung on and fought until Buttercup herself pried his fingers from her sleeve, telling him that a man like Meriadoc shouldn't behave so, and if he didn't stop she'd never let him through her door. Then he stood with a clenched jaw and fists, trying not to cry, as she hugged her foster parents, hugged Meriadoc one last time, said good-bye to everybody, and walked away, Merimac at her side, down Buck Hill and away from her home of nine years.
At Hobbiton, arriving by way of the road from Bywater, Merimac groaning that he ought to know better than to try to match a march with Buttercup, their walking sticks and cloaks coated with dust, they were greeted by an overjoyed Sam, who threw himself into her arms and then pulled her by the hand all the way to Bag End. He talked all the while about how his dad was the gardener at Bag End and how he, Sam, was being taught to do the same someday, and wouldn't that be grand, because then he and Buttercup could spend all their time together, her being a hunter and him being a gardener.
Bilbo met them at his round door, pipe in hand. He smiled, and Buttercup weakly tried to smile back.
Seeing Bilbo, Sam said, “Thank you, Mr. Baggins, sir! Thank you!”
“Thank you?” said Bilbo inquiringly. “For what?”
“For going to get her, sir,” said Sam, and held Buttercup's hand with both of his.