It began with one exchange of thankful notes between sisters, not long after the Great Thaw.

"Thank you for teaching me about love."

"Thank you for all the snowmen we haven't (yet) built in the future."

Then Anna found another little note from Elsa under her door, right before an "early" night (it was already midnight.)

"Thank you for all the chocolate we're sharing together again, just like we always used to do."

Anna grinned–it was wonderful to be doing all they hadn't done for thirteen years. Under the light of a candle, she scribed another little whisper of gratitude.

"Thank you for watching the sky with me whenever it is awake with colour."

She left that one under Elsa's door.

Then, one breakfast, Elsa suggested making a day of notes–hide them around the castle and create a treasure hunt of gratitude. Anna had tried to say something through a mouthful of food, but none of it was comprehensible.

"Swallow your food, then talk," Elsa chided.

Anna choked down her mouthful. "Great idea, Elsa! So, today?"

"What about tomorrow? That way we know we're both ready with all notes hidden."

"Does it need to be all over the castle?"

"Interpret the rules however you like."

Anna clinked her fork against her plate's rim, thinking everything over.

"Can it be many as possible?"

Elsa leaned her chin on her palm, fingertips tapping a light tempo on her pale cheek.

"Five?"

Anna grinned. "Fifty-five?"

Elsa laughed, bringing her cup of tea to her lips with her free hand, sipping once.

"I can't possibly think of fifty-five ways to thank you, Anna. At least not in one night."

"Sure you can!"

"Ever the optimist, aren't you?"

"I do my best," Anna sing-songed.

"Let's say nine. Three squared."

Anna stared. "Three squared. Really, Elsa?"

"I love maths, alright? Three squared."

Anna clinked her fork against her plate in a final peal of agreement.

"Then your three squared it is."

"And one more rule–write down the hidden places. This is a big castle."

Anna nodded, eager to begin. "Consider it done!"

The young Arendellian princess stared at the deepening twilight hours later, drumming the fingernails of her right hand in an adagio beat. Shifting her head against her supporting hand, she re-read the little notes on her desk–all five of them.

"Thank you for Olaf." A small, yet treasured, childhood relic.

"Thank you for saying "hi" at your Coronation party." She still remembered how nervous she'd been standing next to Elsa.

"Thank you for believing in yourself – I knew you could learn to see the magic again."

"Thank you for understanding why I talked to the pictures." She had fantasized more than once that Joan of Arc secretly told Elsa everything Anna had confided in her.

"Thank you for your selfless heart – a good quality in a ruler over Arendelle and, more importantly, in a big sister like you."

Only four more to write and then hide around the castle–she'd try to remember all the locations–and if she didn't, then it made the game all the more fun.

"Thank you for coming with me to our parents' grave to give them a proper farewell. Together." Tears prickled under her eyelids–three years had passed, and yet their deaths still rubbed raw in her chest.

"Thank you for all your warm hugs after so many years." Anna still remembered thawing, and feeling the weight of a grieving Elsa who had, on seeing her alive, embraced Anna in a tight hug, not letting go.

"Thank you for trusting me enough to tell me everything about what had happened the night of the accident."

And then one more.

"Thank you for being the best sister and queen anyone could ask for."

Anna gathered her little slips of paper and slid away to hide them around the castle.

The treasure hunt began straight after breakfast, with Elsa heading down one hallway, and Anna down another, straight for the gallery room, where she flung open the door, making straight for one of the paintings behind which Elsa had hidden a note. Unfurling it, Anna read:

"Thank you for understanding when I confessed what had happened so many years ago."

Stuck in the visor of a stand of armour, another little writing:

"Thank you for always being so cheerful and energetic–it brightened my days to hear you so full of life, as you always are to this day."

Lying on the mantelpiece of the library's fireplace:

"Thank you for being the most loving sister–even when I felt no-one could love me, you did."

Tucked under a jar of biscuits in the kitchen was a fourth sentence of gratitude.

"Thank you for eating chocolate with me under the stars together for the first time since we were children."

Its fifth sibling rested on a large painting of their parents.

"Thank you for mourning with me at our parents' graves, as we should have done three years ago."

A sixth waited for Anna just inside the ballroom's entrance.

"Thank you for still loving me even when I revealed my cur magic."

Anna's heart clenched when she read that scribbled out portion. Even now, Elsa still couldn't quite shake off the thirteen-year belief that her magic was a curse to be feared and abhorred. It was a root in the soil of her childhood that had grown deeper into her psyche for thirteen years. It would not be uprooted so easy, not even with all the love in the world.

The seventh awaited Anna at the head of the spiral stairway that doubled as Anna's favourite slide.

"Thank you for never losing your playful nature even in our thirteen years of separation."

An eighth fluttered at the foot of a clock sitting next to a teapot and chipped cup on a table in a hallway.

"Thank you for still keeping me company on my birthdays and every other days of the thirteen years of our separation."

The ninth–Elsa had made it explicitly clear to save till last–rested under the door of Elsa's room, expertly tucked away in the door hinges. Anna opened it to find just three words written there on the paper, which simply read:

"Thank you, Anna."

A/N: Originally posted for Anna Week on Tumblr, coinciding with Thanksgiving Day (hence the title, which was a prompt for this day) in the States. So to all you American readers: Happy Thanksgiving Day!