This only happens once. Castiel realizes this ten years past the end of the world, gazing at Dean while he sleeps in Cas's bed. The light of the moon illuminates him in silver, and Cas can just make out each freckle on the man's face.

He is immortal. Castiel, angel of Thursday. Well, mostly, anyway.

Dean is not. With each beat of his mortal heart, Cas can feel his life slip just a little further away.

This moment will never happen again. He will never see Dean asleep here on this day ever again, save through memory's imperfect lens.

And that is when Castiel decides that each moment with Dean will be as a treasure. He has enough moments to watch the last stars of the last galaxies burn themselves to ash and cinder, but this short sliver of time will never be repeated.

Everything goes away, not even stars stay forever. Only angels.

He has to make this count.

And that is how, an hour and a half later, Dean finds Castiel covered in flour and sugar, pulling the messiest pie he's ever seen out of the oven.

"I made you a pie," the angel explains somewhat lamely, gesturing to the ingredient explosion in the kitchen.

Dean just smiles and says, "Aren't you gonna serve us up some of that?"
Cas nods, retrieving a knife and slicing them each a wedge of the pie. "It's apple," he adds, sliding the plate in front of Dean.

"Whoa, Cas, this is awesome!" Dean exclaims around a mouthful of pie. "I mean..." he pauses to shovel some more pie into his mouth. "It's heavenly. No pun intended."

Castiel blinks, shifting his vision so he can see the warm glow of Dean's soul. The golden feathering and streaks of silver indicate the truth of his words. "I'm glad you liked it, Dean," he says.

Sam pads into the kitchen drowsily and asks, "Hey, did Cas cook a pie?"

"Get your own angel to cook you a pie!" Dean says defensively, grabbing the pie and curling his arms around it. "Damn good pie."

Sam shoots Cas a knowing smile, his soul shining bright and clear through his skin.

This only happened once.

Castiel reaches one hand out to the bunker's walls and smiles faintly at the memories imprinted in its walls. They both are long gone, Sam and Dean, but sometimes he can almost see them in the halls of the bunker, just out of reach.

No one comes here anymore, not the kids or the grandkids. Dust spirals slowly through the air, and Cas clears it away with a flick of his wrist.

Down in the garage, however, the Impala is spotless, barely showing her age. Cas runs a hand along her side, leaving faint streaks on the paint that he miracles away.

Outside the bunker, the forest has grown tangled over the road, hiding the front doors from view. Cas spreads his wings and lets the faint afternoon sun trickle through the leaves and warm his feathers.

He walks away from the bunker until he finds a small oak sapling. "Hello," he says gruffly to the plant, bending down and running his hand along its soft green leaves.

Without conscious thought, he starts pouring grace into the sapling, feeling it grow and stretch and soar up into the canopy. Acorns fall onto the forest floor like rain. Cas breaks away from the full-grown tree, and it unfolds its last few leaves. The oak is over two hundred feet tall, towering over the others in the forest.

Castiel sighs softly and leans against the tree, wings brushing the ground.

He remembers baking pie a hundred years ago, moose jokes and demon jokes and counting Dean's freckles in the early hours of the morning when everyone else was asleep.

He remembers the end of the world (multiple times), eternal Tuesday afternoons, listening to Metallica in the Impala.

It only happened once, but he made it count.

It is a Thursday when Castiel returns for the last time.

The bunker is long forgotten, and only the constant efforts of a lonely angel have kept it from sinking into oblivion.

Cas sits down in the Impala's cracked leather seats and turns on the music. It's Led Zeppelin.
He leans close and smells the familiar black leather, but he can't smell Dean at all, only age and dust.

Cas leaves the music on and flies to the kitchen, hands automatically reaching for the cabinets. Flour, eggs, sugar... They appear in his hands, magicked in from afar.

The warm, cinnamony scent of baking apple pie fills the bunker's old, dark halls for the first time in uncounted years.

Cas takes it out of the oven and admires its golden crust, cooling it with a wave of his hand and cutting two slices.

He sets one out on the counter with a fork next to it before he remembers, and Cas cries in the kitchen with a slice of pie in each hand, hot tears dripping onto the plates.

It only happened once.

Dean only happened once.

It is a Thursday when Castiel leaves for the last time, the kitchen light still on. The pie still waits on the counter for a man who will never return to eat it.

Cas doesn't have a soul, but he could swear he does because it aches so much.

He can hear the faint sound of Dean's favorite song echoing through the bunker's empty halls, the smell of fresh-baked pie hanging in the air, and for a moment, for one single moment he can hear Dean coming down the stairs for breakfast, he can hear Sam listening to the morning news.

And then the moment is gone.

A sense of emptiness washes over Castiel, as cold and deserted as the bunker.

He spreads his wings and flies up, into the clear blue sky. He is in heaven a moment later, calling Dean's name.

And then he sees a flicker of silver and gold, and eyes greener than spring.

"Cas?"

The angel flies over to Dean and wraps his arms and wings around him like he never wants to let go. "Dean," he whispers.

"Cas, buddy, what took you so long? We missed you. I missed you." Dean runs his fingers through Cas's hair.

"I had to take care of something," Cas says lamely. "The children..."

"For two hundred years? Without a visit?" Dean asks, pressing his mouth to Cas's cheek.

"If I had, I would never have left," Cas answers, burying his face into Dean's soft hair. "I'm never going to leave again."

It only happened once, that an angel and a human (who was once a demon) lived together for many years.

And on the last Thursday that angel spent on Earth, it continued where it left off, and never truly had to end.