Dean had always been suspiciously modest, even before he and Sam were teenagers. He never undressed in front of Sam. He never wore tight clothes.
Sam had never put much thought into it.
All of that had changed a few weeks ago, when Sam and Dean were hunting a shapeshifter. Before Dean could kill it, the shapeshifter had said, "Don't you ever wonder why your brother, the person who loves sex so much, is such a priss about people seeing him naked?"
Sam hasn't been able to stop thinking about it since. It's a valid point. Dean, the person who has had more sex than anyone Sam's ever known, hates other people seeing him naked. How does that make any sense?
Sam wasn't trying to be perverted or creepy, but he couldn't stop thinking about it. He tried asking about it and, as you would assume, Dean had brushed him off saying 'I'm fine' and that 'Shifters lie.'
In the past few weeks, Sam has tried every one of his plans… and sadly, none of them have worked. He realized that he would have to do this the hard way, the thing that he knew he would have to do, but had been dreading since he began this mission. He would have to 'accidently' walk in on Dean while he was naked.
Sam and Dean had finished their latest hunt, a werewolf who was reeking havoc in a small town, and Dean, as usual, went to the bathroom, yearning for a long, relaxing shower. Sam heard the water turn on. He waited a few minutes before picking the lock, and slowly, as quietly as he could, opening the bathroom door.
Dean stood, back facing the door, as he washed his surprisingly curvy figure. From behind, Sam could see a thin, hourglass-shaped waist, a round bubble-butt, and what could only be described as womanly shaped hips. He froze, flabbergasted, as Dean turned around, revealing a full chest of large, perky breasts. He gasped when instead of the penis that he was expecting, the sight of a small, clean-shaven vagina sat between Dean's legs.
Dean is a WOMAN? How in the hell did he hide that? What the fuck is going on? Is this some kind of sick joke?
Dean had always had a feminie face, one that had rightfully earned him the nickname 'pretty boy' - doe-eyes, long eyelashes, and naturally plump, pouty lips - but Sam, obviously, because who would, had never thought 'Oh, maybe my brother is secretly a girl!'
Sam locked eyes with an equally horrified Dean.
"GET OUT!"
Dean demanded, reaching down to cover as much of his body as he could.
Sam left the bathroom breathing heavily, mind filling with questions. Within a minute, Dean was stumbling out of the bathroom, a towel wrapped tightly around his… her?... body.
"What the actual fuck, Dean?"
Dean looked down, "God, Sam. How much did you see?"
Sam scoffed. As if that was the issue right now!
"Enough to know that my brother… or whatever the fuck you are… has a pussy. What the fuck, Dean?"
His brother… sister?... sat at the end of the bed, "It wasn't meant to be secret, Sam. I promise. If it had been my choice, I wouldn't have hid it from you. In fact, if it had been my choice, I wouldn't be pretending to be a guy in the first place."
Sam had no idea how to feel. He felt angry and betrayed because his brother… sister?... had lied to him for so long… but overall, he felt confused.
"What do you mean, 'if it were my choice?' I have so many fucking questions, Dean."
Dean sighed, "Go ahead. Ask 'em. I swear, I'll be as honest and open as I can be."
"Who's making you pretend to be a dude? What's your real name? What the fuck?"
Dean chuckled sadly, "When mom died, dad decided that he didn't want a daughter. He changed my name from Dianna to Dean. He changed my pronoun. He changed anything that made me even remotely girl-like. Anytime I corrected him, he would beat me. God, you wouldn't believe the beating I got when I started my period. When my boobs started growing, he bought me one of those binders that transgender people wear, and forced me to wear it. I wanted to tell you, but dad wouldn't allow it."
Sam clenched his jaw, feeling a wave of justified anger toward his father.
"That isn't fucking right, De. I'm sorry."
Dean looked down, "I wanted to be a girl so bad, Sammy. Still do. I wanna grow out my hair. I wanna paint my nails, and flirt with hot guys. I wanna be a normal woman. But at the same time, I'm really scared. Anytime I think about wearing something that shows my boobs or butt, I remember dad hitting me, and then, I feel like I'm doing something wrong. I wish I could just be normal. I wanna be a woman so bad. But I can't."
Sam hugged his sister as she sobbed into his chest. He ran his fingers through her spiked, blonde hair.
"Come on, De. Dad's gone. This is your chance."
She looked up, "You really think so?"
"Yeah, trust me, Dianna. I do."
His sister smiled at the sound of her old name.
"I want that more than anything."
TEN YEARS LATER...
Dianna sat on the couch beside her beloved husband with him rubbing her large pregnant bump, watching as their five kids and nephew played. Sam was seated beside her, practically squashing his poor fiance.
Once Dianna's true gender had been revealed, Sam felt it was appropriate to (finally) come out to her. Much to Sam's shock, Dianna wasn't surprised, disappointed, or upset. She told him that she loved him more than anything, had always assumed that he wasn't totally straight, and came out as bisexual herself.
The Winchester siblings stopped hunting. They settled down in a small town in Massachusetts. Sam got a job at a small book-shop, and three-years-ago, when the owner died, he began running the shop himself.
Dianna got a job at a local bar, where she fell in love with the owner, a blue-eyed man named James Novak. They got married after two years of dating, and had their first child, Benjamin Samuel Novak, shortly after. Within the following seven years, Dianna had been pregnant with and given birth to four more children, Addison Mary Novak, Michelle Emma Novak, Matthew Robert Novak, and Owen Gabriel Novak.
Sam met Gabriel at a bar five years after Dianna and Castiel got married. They hit it off and dated for three years before they got engaged. The wedding wasn't important to either of them. So, they haven't gotten married, but at some point, they will.
Obviously, as a gay couple, Sam and Gabriel couldn't have children of their own, but Dianna gladly offered to be their surrogate - using Gabriel's sperm and her egg, they created child that was related to both Sam and Gabriel, Oliver Dean Winchester.
Dianna's currently eight months pregnant with their second, and final, child - another little boy, who they plan on naming either Ethan or Thomas.
Dianna and Castiel live in a large, colonial-style house, which was the perfect size for their large, seven-person household. Sam and Gabriel live across from them, in an equally as large, modern-style house.
Life was perfect, just perfect.