When she was born, no one in the whole kingdom of Arendelle suspected that their newest princess was cursed with eternal winter. Of course, it soon became noticeable, and then started the siege that would bring years and years of misery.
When she hurt her sister Anna for the first time, that was when the Guardians were seriously concerned about her fate, and sent Jack Frost to see. Their powers were not dissimilar, and little Elsa, still only a child, delighted in his company.
When she was eight, and not yet accustomed to being separated from her sister, she would lay crying at night because she wanted to build a snowman. And even the ones that Jack made for her felt unsatisfactory to him, so his attempts to cheer her up did not work.
When she was nine, and staring blankly at the ceiling while her sister called at the door, Jack made animated ice sculptures, and taught her how to control her powers to allow her to finally, one day, open that door. He also tried to visit her more often, although he shirked some of his duties to do so. That year, Canada received surprisingly little snow.
When her tenth birthday had barely begun, Jack whisked her outside to the Northern Mountains to have a bit of fun flying. Neither was cold, even with the sharp winds blowing, because they had each other and they had someone who understood. Elsa spent the morning happily creating snowmen until she suddenly remembered Anna and then it wasn't fun anymore, so they went back.
When she was eleven, the future queen of Arendelle no longer cut off her laughter, but she also no longer cried when Anna came knocking again. Jack thought, at that time, that perhaps she was saving her tears.
When she was twelve, Elsa taught Jack how to play checkers and chess, how to give nice hugs, and Jack would you please stop distracting me while I'm studying. Elsa, if asked, would have replied that Jack Frost was her best friend – not that she ever said so, no matter how many times Jack tried to interrogate her.
When she was thirteen, one morning a frantic Elsa threw her hairbrush at him in an effort to get him out of her room, to which he quickly complied. Later, with a throbbing on his temple and a question on his mind, he watched as the Queen came in and had a serious talk with her daughter, and after that these hairbrush-throwing episodes came monthly.
When she was fourteen, Jack stopped laughing and his eyes were tighter, watching, waiting for the morning when Elsa would never see him again. Unbeknownst to him, they still had a few years left, and after a few months and an epic sulk, things went back to normal.
When Elsa was fifteen, her father threw a tiny, minuscule party for her, with only a few chosen guests invited. Halfway through the dancing, Elsa stumbled away from her partner and ran to her room, where Jack found her huddled beneath her blankets, with a snowstorm raging and windows cracked and holy mother of god, when had her powers grown so much that icicles the size of chairs could jut out from the floor?
When she was sixteen, there was no party.
When she was seventeen, relations between her parents and Anna had not improved, nor had the rumours from the villages abated. Elsa never cried, but her days of fun were gone, until Jack returned from his duties to laugh and be her best friend again.
When she was eighteen, Jack noticed that she had grown, like really grown, into a beautiful young lady, and after that he became a little awkward running into her room without knocking and lying next to her on the roof to count stars.
When she was nineteen, and bereaved by the loss of her parents, Jack was there. He would've been the King of Fools for her, if only to make her smile. Neither noticed a lonely princess on the other side of the door, listening to the sound of her sister's laughter.
When she was twenty, and began having a line of suitors trailing after her, Jack left for a few weeks to calm down and to temper his jealousy of having to share his – friend? He didn't know what she was to him anymore, and all he knew was that some of the people she met were seriously annoying.
When she was twenty-one, her coronation came, and thankfully nothing happened. The other Guardians told Jack that his duties to the other children were more important now, since Elsa wasn't even a child anymore, but Jack didn't want to leave her, even if she was happy with Anna, together.
When she was twenty-two, her marriage engagement was announced.
On the day of her wedding, he walked up the aisle to her, invisible to everyone's eyes, and kissed her softly, just once. Then he was gone, and never returned.
One the day of her death, the room was filled with close friends and family, with Anna and her husband and children sobbing, and Elsa lying there peacefully after seventy years of life, with a few bumps but on the whole, a happy life. Jack floated up and touched her face, but she could not see him anymore. All Elsa knew was that before she fell asleep, there was the touch of cold, the touch of old, the touch of a long-lost love. And it was more than enough.
In summer, the kingdom of Arendelle mourned heavily, and for a few months pictures of Queen Elsa were scattered everywhere, making it impossible for Jack Frost to stay there long.
In autumn, when the crisp cool air first blew in from the mountains, Jack returned with it, and prepared for his mourning.
In winter, that year was the harshest, where ice formed in jagged edges and snow fell like tears, and that year was when Jack Frost truly became believed in.
In spring, Jack went to the castle where he'd spent two decades fluttering around, like a moth drawn to the flame, and he visited Elsa's old bedroom and saw all her dresses and gloves and memories, and that was when he first cried.