At first, it's easy to assume that he'd roll with things just like he's always done. After all, he's used to the routine: wait for things to play out and enjoy every scrap of novelty you can find.
That's why Sans is startled, when they finally — finally — end up on the surface, and he cares. And the force of it chokes him up — just like when he was tiny and left the Labs for the first time in his life. The world suddenly seemed so big back then.
Well, it's endless now.
And he's terrified of losing it all.
That's why that night — their first night on the surface — when they're settling for sleep, for once it's he who cuddles up to his brother for comfort and not the other way around.
He's terrified of opening his eyes in the morning too. Terrified of everything being… not there anymore.
But it's still there. They're still on the surface. Time is still moving forward.
The first days are hectic and filled with emotions and construction work, and politics, and paperwork. Everyone's busy, everyone's hard at work, yet Sans still has time to worry — especially as he sees the kid grow wearier each day with all the responsibilities piled up on them — ambassadorial or not.
Will they snap? he wonders. And then it turns into, When will that happen?
"Do you have a pen?"
That snaps Sans out of his mindspace, where he's stuck somewhere between ruminating over their fates and figuring out how to cook a dinner for fifteen people in half an hour.
"Huh?" he says, turning to face Chara.
"Do you have a pen?" they repeat. When he doesn't respond, they add, "Mine is out of ink."
Absentmindedly he notes how they keep worrying the hem of their sleeve. "Uh, pen? Yeah. Yeah, let me just..." He pulls a pen out of his storage.
"Thank you." They snatch it out of his hand and instantly pull a palm-sized piece of paper out to scribble on it.
Sans recognizes a pocket-sized calendar, and Chara is currently busy scribbling out one of the numbers.
Then they look up and meet his eyes.
"It has been eleven days," they say and give him a small smile, as if that explains everything.
In a way it does.
At the very least, the night that follows is mercifully dreamless.