The year he turns thirteen, Jamie worries.
He's heard the Guardians talk before. He knows that children inevitably stop believing. He doesn't know when it will happen though, and the day he officially becomes a teenager seems a good candidate.
He talks with Sophie and impresses on her the importance of the fact that no matter what happens, she must convince him that Jack Frost is real. He scrawls the words all over his room, and he gathers all the evidence he has of Jack - every picture, every journal entry, every gift. He goes to sleep with the words repeating in his mind like a mantra.
Jack is real. Jack is real. Jack is real.
He wakes up with the words still repeating in his mind, and he believes them, wholeheartedly.
He watches the clock after that. He was born at exactly noon, so maybe -
At 12:05, he gives Sophie a thumbs up. He still believes.
When Jack shows up that night, grinning and wild and with a wonderful present straight from North, he doesn't mention his fears. Jack was alone for so long, he doesn't want to worry him.
But he worries, all the same.
He isn't sure if the others will still believe. He's always believed more readily, after all, and he had been the first. Maybe he's a special case.
But even though Cupcake is actually fourteen now, she still waits for Jack just as eagerly. None of them give him funny looks when he brings Jack up, and all of them love him as much as ever. Everyone still writes to North, and everyone still hunts for eggs, although they pretend it's for Sophie's sake now.
They check and double check, but they all still believe.
He wonders next if it's hurting them somehow. He doesn't mind for himself - Jack needs believers more than Jamie needs to become a stereotypical teenager - but for Sophie, for the others, he wants to at least know.
But Pippa and Caleb start going out, and he's got a crush on a cute girl at school, and everything seems normal. They keep their belief between themselves, and no one seems to think they're any different than the rest of their grade.
Jack comes every week, sometimes several times a week, and he looks a bit younger than them now, but Jack's been around for three hundred years. He's no less mature than them; he just hides less from them now.
Like when he's gone for two weeks and comes back covered in blood, only some of which is his.
There are more monsters than Pitch in the world, Jamie learns, and he cleans Jack up and sends Sophie for bandages so she won't have to see the worst of it.
When Jack's alright and they can all breathe again, it occurs to him he can cross another fear off his list. He'd thought maybe it was Jack's constant visits that kept belief fresh, but two weeks have passed, and when he calls the others to tell them what happened, they're response is to pile into Monty's car to come check on Jack.
Cupcake's seventeen, but they all still believe.
Eighteen, they agree, is probably the absolute limit. There's no way they'll make it past eighteen.
They celebrate Cupcake's birthday like it's a funeral, but twenty-four hours later, she finally snaps, "Stop staring at me. I still know Jack's real."
A weight lifts off Jamie's shoulders. "Cheers," he says, lifting his soda.
The others follow suit. Jack shows up, apologizing for his lateness.
Seeing as he brought Cupcake chocolates from France, he's instantly forgiven.
Twenty-one? they venture with hesitant guesses. They'll be on their own then, not even conceivably children.
They go off to college, some to the same one, some states away, but they stay as close as ever, bound by common secrets. Sophie sounds nervous every time she calls, but they all still hold the same truths to be self-evident: The Guardians are real, the Guardians deserve to have more believers, and Jack is surprisingly helpful with homework, particularly history papers.
Jamie plans to teach, but he wants to be a writer too, so he can get Jack more believers. Monty wants to go into the movies, Cupcake draws, Pippa wants to run a daycare center, Claude wants to design ornaments, and Sophie wants to write like Jamie, but they all want to get the word out on Jack.
They're graduating college, and they still believe.
When Pippa has a kid and sees Jack when he shows up with a big grin and yet another present, they more or less give up. If they're not adults now, they never will be.
Jamie finally gets the nerve to ask Jack about it.
Jack laughs, high and startled. "I asked North about that years ago," he says with a wide grin. "I can't believe you didn't just ask me."
"We didn't want to worry you," Jamie mutters.
Jack raises his eyebrows. "Jamie, you first believed during the middle of the biggest crisis of belief the Guardians have ever known. I worried about that from day one."
"But?" Jamie prompts.
Jack shrugs. "When I tell you something, do you believe me? When I say I'm going to try and protect all the kids I can, do you believe in me?"
Jamie's mouth drops open.
"You don't believe I exist," Jack points out. "You know it. That kind of knowledge doesn't just vanish. You believe in me in other ways. Perfectly adult ways," he adds with a grin.
"Oh," Jamie finally says.
"Oh," Jack agrees wryly. "Any other questions you've been carefully not asking me for the past twenty years?"
"Not for the past twenty years. But I've been working on my next book and if you've got a moment . . . "
Jack smiles fondly as Jamie rummages for his papers.
The kids had fought for them against Pitch himself. A core memory like that was too powerful to ever forget.
At least, that was what the others said, and Jack is inclined to believe.
A/N: Yes, that was a small Inside Out reference at the end.
I was tired of angsty "Jamie forgets" fics, so I wrote this as a sort of answer to them. Don't get me wrong, some of those fics are beautiful, but I wanted something happier.