The first thing he saw, as he was walking down the stairs, was his brother sitting next to the table.

Dean had turned the chair, so its back was against the table, and he was just sitting there, completely still, resting his elbow on his knee, his hand covering his mouth, staring at the staircase.
He didn't acknowledge Sam in the slightest, never moved a muscle until Cas walked in and was coming down the stairs.
That was when Dean lifted his head. "Cas, did you get to him in time?"
Cas nodded.
"No deal?"
"No, I killed the demon just before they closed it."
"Good."
Sam raised his voice, striding straight over to his brother, towering over Dean's sitting form.
"Good? Good? How is letting an innocent die needlessly a good thing?"
Dean stood up slowly, as if any sudden movements was going to shatter him. "Because it means that you stay alive, Sammy."
"Who cares?" Sam spat the words out.
"I do, dammit!"
Sam was yelling now: "I wasn't doing anything you haven't done before."
"That's different!"
They were almost chest to chest now, both yelling.
"It's not any different"
"We agreed, no one makes any more deals, never again"
"It was the only way."
"We could have found another way."
"There wasn't time."
"Too bad, then, but that doesn't mean that you get to deal yourself in exchange."
"Why not? I don't matter!"
"You do to me! I'm not going to lose you!" The word "again" hang unspoken in the air.

Dean's shoulders suddenly slumped and he stepped back a bit. "I can't go on without you, you, me, Cas, we are all that is left."
Sam stared at his brother. "I thought …"
"No, you didn't think. That's the problem."
"When Charlie died, you said that it should have been me, so I …"
Dean uncoiled like a spring and without warning punched Sam in the jaw with a hard hook, that had Sam stagger back half a step. He shook his head, a bit dazed, then faced Dean again. "Ok, do you feel better now?"
Dean's answer was to punch him once more, making his mouth bleed. Dean lifted his hand again, but suddenly his wrist was grabbed, almost throwing him off balance, as his forward motion was abruptly brought to a stop. "The Hell?" He glared at the interference and was met with an implacable stare from intense blue eyes lighting up with angel power.
"Dean, stop that. You do not punch your brother. Calm down."
"Calm down? Calm down? If it wasn't for you, he would be lost in all ways"
Cas' answer was to simply grab Dean and drag him out of the room.
Sam sat down on the chair Dean had abandoned, and took a couple of deep breaths, trying to calm himself down, touching his bruised face carefully. Leaning back he closed his eyes wearily and just waited.

When Dean walked back into the room, he was obviously still angry, but was holding himself in check with an iron will.
Sam opened his eyes and looked at Dean warily. "You gonna punch me again?"
"Nah, no punching."
"Gonna keep yelling? Cause my head really hurts."
"Nope, not gonna yell either. I'm planning on a more hands on kind of approach."
Sam moved uneasily in the chair. "Uhm, eh, wha'?"
Dean moved closer, slowly, his whole body language an unspoken threat. Nervously Sam stood up and moved a bit backwards.
"Dean, what's going on here?"
"Bend over the table, Sammy!"
"What!? Why? No way! You can't! I'm not 15 anymore and you are not Dad!"
"Oh, yea? But when you act like a 15-year-old, you get treated as one, and you better be glad Dad isn't here!"

Sam stepped back again, as Dean got closer, dipping his head and looking up at his brother, which is quite a feat for someone 4 inches taller than the person, he is looking up at. "Uhm… Dean?"
"Oh, no. The puppy dog eyes are not getting you out of this one, Sammy!"
On automatic response Sam said: "Don't call me Sammy," reverting to his 15-year-old self in both words and tone.
That realization threw him off for a beat, and that was all Dean needed.

He lunged, grabbed Sam by the arm, kicked him off balance with a foot behind his knee, quickly turned and pushed. In a blink of an eye Sam landed hard on the table, the air leaving his lungs in a "Wooof," his arm twisted high up behind his back, Dean holding his wrist tightly.
Before Sam had regained his breath, Dean's elbow landed on his neck, pressing roughly down even as Sam started struggling, using all his considerable strength. To no avail. Dean had the upper hand and he had Sam securely pinned.

With his free hand Dean undid his belt buckle and the distinct sound of a leather belt waving "Bye-bye" to a pair of jeans sliced through the air, making Sam freeze. "Dean, please, don't."
There was no answer, but Dean did let up some of the pressure on Sam's neck as he felt the struggle leaving his brother's body.
Sam hid his face in his free arm and took a deep breath, trying to get some of his wind back, knowing from experience that he was going to need it soon enough.

Then the doubled-up belt landed for the first time, hard across Sam's ass, making him groan in surrender.
Dean kept the belt in motion, strikes landing heavily from the top of Sam's ass down his thighs to above his knees. After the first round Dean let go of Sam's arm, and Sam didn't even try to get up, he just pulled his arm in front of him, curling it over the back of his head, heaving for breath in between strokes.

Seeing that his brother accepted the punishment Dean stopped after just a few more strikes, mentally crossed his fingers and said firmly: "Sam, drop them."
Sam flinched, but carefully pushed himself off the table, undid his belt and fly, pushing his jeans to his knees.
He sent Dean a sorrowful glance, then compliantly bent back over the table, folding his arms in front of him and burying his face in the crook of his elbow.

Cas watched silently from the kitchen entrance.
He wished he didn't have to, but he felt the need to make sure that Dean had his anger under control. Cas knew that most of Dean's anger was really fear and it had taken a lot of effort to talk him down from the full-blown explosion that had been well on its way before Cas stepped in.
At least this was marginally better than Dean punching the crap out of Sam with his fists.
As Cas keep his vigil, Dean's belt continued its grim dance all down Sam's backside. First leaving red stripes down his legs, then the stripes blooming into welts, then into welts on top of welts.
At first Sam kept amazingly still, not moving to avoid the strokes, just grunting a bit, but inevitably, as the fire built, small desperate movements started escaping his control.
A foot stamped, a leg jiggled, his hips wriggled from side to side, he rocked his body forward, slamming his hips into the edge of the table, at one point he half rose from the table, only to have Dean put a hand on his back and shove him back down.
The ragged breaths and small grunts turned into yelps, then to pleads, which finally dissolved into sobs, as Sam just gave up, stopped trying to fight the pain and simply lay there crying, waiting for the ordeal to be over.

Seeing this Dean brought things to a close with five quick, hard strokes all aimed directly at the point where ass meets thighs, knowing from personal recollection that the welts left in this area would make themselves felt for a few days every time Sam sat down.

Then he stopped and let the belt fall to his side, breathing heavily from exertion. After a beat, he placed a gentle hand on Sam's back, and when Sam's sobbing muted enough that Dean assumed his brother was able to listen, he said quietly: "Please, don't ever make me go through something like that again. Please, Sammy."
With a deep groan Sam shoved himself up to a standing position and gently held his hands against his ass, feeling the heat waves through the thin cotton. "Dammit, I had forgotten how much this shit hurts. Did you leave any skin back there at all?"
Dean didn't answer, just kept looking at Sam, belt dangling limply in his hand.
Sam stared back at him, then he said quietly: "Yeah, ok, I get it. Goes for you too, though, ok? No more giving yourself lethal injections to talk to ghosts, ok? Because next time you do something like that, I'm going to take a page from my big brother's book! Capice?"
Dean grinned crookedly. "That is the kind of deal, I can go in for, so yeah, deal, Sammy."
Then he reached out to grab his brother by the neck and pull him into a hug.
As they released each other again Dean added: "Oh, by the way – I'm sorry about punching you. I shouldn't have, that was wrong. I'll give you a free one, come on?" Sam shrugged. "Nah, it's ok. Besides I don't feel like punching anything right now, I just want to sleep."
Dean grinned unexpectedly. "Yeah, I had forgotten that part– a dance with the belt really is tiring, isn't it? Go ahead, I'll go do some research, try to find a lead on Jack."
Sam groaned his way through kicking off his boots and jeans, then moved slowly, gingerly, off to his room.

When Sam was out of sight, Dean turned to Cas with a deeply unhappy look on his face. Cas stepped into the room and lifted an eyebrow questioningly, trying to figure out what was going on in his friend's maelstrom of a brain, because it was obviously spinning into a downwards spiral, which was never a good thing with Dean, because Cas knew from experience how difficult it was for Dean to drag himself out of such spiraling, and the" cure" usually relied way too much on booze, bacon and bullets.
"Dean," he began tentatively, "What are you thinking?"
Dean wriggled his shoulders uncomfortably. "Just thinking about my dad."
"How so?"
"It's my job, you see. It's always been my job. Take care of Sammy."
"And you did, Dean, you did, and you do."
"But I didn't, don't you see? If you hadn't been here, able to zip right to him, he would have been lost, dead, gone forever. And then I punched him. I punched him. I shouldn't punch Sammy."
"No, you shouldn't, but you were angry, Dean, so you made a mistake."
"Do you know what my dad would have done if he was here?" Dean shuddered. "I wouldn't be able to sit for days, I would count myself lucky to have any skin left on my ass after he got done with me! I punched Sammy, Cas, I, I …Take care of Sammy, that's always been my job, don't you see?"
"Dean, you do realize that you can let others help you with that job?"

Startled Dean stared at Cas, who continued, his voice suddenly even more gravelly than usual. "And who takes care of you, Dean?"
Dean looked crestfallen. "Wha?"
"You can let us take care of you too, Dean, don't you see?"
"Wha?"
"We are your family, Dean, family takes care of each other."
"I punched Sammy, Cas"
"And he forgave you."
"But I didn't!"
Cas sighed. "No, I guess not. You never do, do you? You just keep carrying the guilt around. You never let it go."
Dean shrugged and blew air out his nose: "I guess not, not since Dad…" His voice trailed off.

Cas frowned. "Are you saying, what I think, you are saying, Dean?"
"Uhm…"
"Really, you think taking care of you involves... "
Cas trailed off and gestured towards the belt Dean still had dangling in his hand.
Dean shrugged, then impulsively stepped forward and held out the belt to Cas, who stepped back in surprise.
Dean didn't give an inch and the tableau held awkwardly for a stretch. Coming to a sudden decision Cas almost ripped the belt out of Dean's hand and cursed in a decidedly un-angelic way.
Dean held eye contact a moment, then whirled round, jerked his jeans down and put his hands flat on the table, gazing down on the initials carved into the surface.

He felt Cas' hand on his back, roughly pushing him down until his chest was flat on the table. Dean, unknowingly mirroring his brother, folded his arms and tucked his face into his elbow, steeling himself to get through the punishment he both wanted and didn't want.

Cas hesitated, wondering how on earth a warrior of the angelic hordes had ended up staring at the boxer clad hind end of a hairless ape, preparing to lash it with a leather belt for some obscure reason having to do with relieving guilt and idly wondering if calling a priest to take Dean's confession would be a viable alternative.

Dean shifted uneasily, then broke into Cas' reverie by mumbling. "Waiting is the worst part, are you going to keep me wai… yick."
The first stroke breaking his sentence off and startling a yelp out of him. Taking his cue from the earlier scene, Cas whipped the belt up and down Dean's ass and thighs, gritting his teeth to keep his resolve, waiting through the stiff-necked silence, the steadily increasing involuntary movements, listening to his friends' breathing getting more and more ragged until he saw Dean bite down on his wrist to muffle the small sounds of distress that was rapidly turning into sobs.

Cas dropped the belt, seized Dean by the upper arm, pulled him up and into a hug.
He held him there until he felt the tension drain out of Dean's body, then pushed him to arm's length and said seriously: "You are forgiven, Dean. Do you believe me now?"
Dean nodded.
Cas searched his face and added: "Do you forgive yourself?"
Dean avoided Cas' eyes for a beat, then met them squarely and with a look of surprise nodded.
"Yeah, I think, I do, actually."
There was a silent moment, then he added "I'm sorry I made you do that."
Cas smiled genuinely. "So am I, but as I said – we are friends, we are family and I will take care of you, whatever it takes. I've got your back."
Dean huffed out a breath. "I think you mostly got my ass, to be precise!"
But then Dean leaned back into the hug and they clapped each other roughly on the shoulders in one of those testosterone-laden manly hugs that almost look like a wrestling match about to start.

Afterwards Dean bent down and reluctantly pulled his jeans up over his sore legs and ass, letting the fly stay open. He looked at the belt on the floor with distaste. "Yeah, not wearing that again," he mumbled.
Cas picked it up and snorted. "I'll just hang unto it then, apparently it is a helpful item."
Dean just shuddered, then turned around and, moving stiffly, made his way to his room, presumably to take a nap, lying on his stomach.