Undying Love

Richard Castle can truly say his love story with Kate Beckett is eternal; Caskett Soulmate (Semi) AU - Set mid-S5

A/N: This will be 2 parts. Prompt at the bottom.

Stepping off the elevator on his floor with a slight spring in his step, Richard Castle whistled as he walked the remaining few feet to the front door of his apartment. He'd just picked up coffee and pastries from his favorite bakery and was bringing them home to where his gorgeous and incredible girlfriend waited—hopefully still in his bed. Seeing as she had already agreed to have a lazy day with him, he was one hundred percent certain that day would be an amazing one.

For Castle, the prior seven months of his life had been a wonder—ever since Kate Beckett turned up on his doorstep with soaking wet hair and gave him a kiss he was certain he'd remember to his dying day. That moment—and the incredible night that followed—solidified them as a couple, and there had been no turning back. Every bump in the road they encountered only served to make them stronger and with each day he woke up beside her Castle felt more joy in his heart.

On that chilly January morning, Castle and his companion had agreed to do absolutely nothing. There was talk of sitting on the couch and watching some movies or perhaps finding a recipe to craft together. And, obviously, he had suggested spending the better part of the day under his flannel sheets without wearing a stitch of clothing. Or, in his mind, they could do some combination of all those things; as long as he spent the day with her he would be happy.

When he arrived at the front door, Castle brought the bag of pastries up to his mouth, clamped his teeth around the folded flap, and then dug into his coat pocket for his key FOB. Once he used it to unlock the door, he slipped inside, and began trying to shrug off his coat while still juggling pastries and the carboard carrier that held their two coffees.

"Beckett?" he called out to his companion, not sure if she would still be in bed, where he'd left her half an hour earlier. Knowing Beckett, he didn't think that was likely, though he didn't see her in the kitchen or the main sitting room.

"Where are you? I got one of those cinnamon rolls you like so much."

When he didn't hear her respond verbally, he thought she might be in the bathroom, so he walked into the bedroom to see, but then he caught sight of movement through the walls of the bookshelves. Crossing into his office, he found her crouched behind his desk, her back to him, evidently so engrossed with whatever she was looking at, she didn't even look up when he came in.

"Whacha doin'?" he asked playfully, but when she turned around and he caught sight of what she held, all delight dropped away from his face and his heart began to sink towards his shoes like a rock thrown into a shallow lake. "Ah…Kate…"

"What is this?" she demanded, her tone sharp as she held out the aged photo album containing his most precious possessions. Castle was immediately torn between coming up with a plausible answer to her question and begging her to be careful with the delicate item she held.

"Wha…um, where did you find that?" he asked as a way to stall so he could collect himself enough to recount the explanation that had been poised on the edge of his lips for months.

"I…" She glanced between him and the photo album for a moment and then continued. "I was looking for a book to read today and I accidentally knocked a stack over. This was jammed in behind them. What is it?"

"Well." He placed the coffee carrier and pastry bag on the end of his desk. "That's kind of a long story."

"Why…" Again, she looked down at the album with utmost confusion. "Why do you have fake pictures of me in old timey costumes?"

"They're not fake."

She didn't blink. "Clearly they are. What the hell, Castle? Is this part of some bizarre Nikki Heat research project? Or-"

He held up his hand and she stopped speaking abruptly. Though his heart still raced beneath his ribs, Castle managed to calmly say, "Will you please let me explain?"

Kate's face grew noticeably paler and her brow filled with wrinkles. Taking a tentative step forward she asked, "Rick, what's going on?"

"You're probably going to want to sit down."

"No. I want you to tell me. Right now."

He wasn't surprised at her sharp tone or her refusal to do as he asked; her reaction was almost always the same. Instead of letting it throw him off, he merely stepped forward, pulled the album from her grasp, and turned forward two pages to find the only photo that would help prove his case. "The pictures aren't fake, Kate; they're real. That's you and me during one of our many lives together." He turned the book so that she could see picture from 1884. It was black and white, tattered at the edges, and very faded, but there they stood, stone-faced in front of one of the first cameras in existence.

Instead of being amazed, Kate's response was filled with derision. "What the hell are you talking about?"

"I'm trying to tell you that I'm not Richard Castle. Well, not just Richard Castle. I've actually been-"

"God, Castle! Seriously? Seriously?!" Kate threw her hands up in disgust as she walked around to the other side of his desk. She folded her arms over her chest and snarled at him. "You're pulling this shit on me now? Seven months together and-"

"Kate. Please." He continued, soft and patient. "I need you to just trust me for ten minutes. I know this is going to be hard for you. It...it is every time."

"Every time," she echoed flatly.

"Six...This is the six time we've had some version of this conversation," he said, managing not to convey the weariness he felt in his tone. Not that he didn't love and appreciate his life—he absolutely did, but he would have appreciated one go-round without Kate's initial reaction being betrayal and rage. Then again, Kate wouldn't be Kate if she didn't react that way. At least this time was the first she'd discovered the photographs; that at least brought a little newness to the déjà vu like scenario.

"What does that even mean!? You're not making any sense!"

"It will; I promise," he said. She gave him one of her most impatient expressions and he stepped around to the other side of the desk to face her. "I was born in 1750 as Alexander Roberts. My mother was a poor, practically destitute woman. She had an affair with a gentleman who was, we'll say, of a magical persuasion. As a result, I am, in a colloquial sense, immortal."

She blinked once. Then again. "You're immortal?"

"Yes."

"You were born in 1750?"

"Yes."

"And why in the hell would I believe that?" she demanded.

He simply shrugged. "Because it's true. I've lived a dozen different lives...seven of them with you. We met in 1765. You were Katherine Grant back then. We...fell in love, married, and lived very happily together until 1799, when you died—the first time. When I found you again in 1818 I couldn't believe it. You were Katherine Holbrook that time, but it was still you."

She arched one eyebrow at him. "You're trying to say I'm immortal too?"

"No, no." He shook his head and explained what took him the better part of two centuries to piece together. "It's your soul; reincarnations of your soul. We're soulmates, so somehow your soul keeps finding mine, or mine finds yours. Regardless: we find each other. I'm me, and you're someone different, though somehow you're always named Katherine and you always die far too young."

She stared at him for thirty seconds and then swallowed hard. "You…you're serious."

"I am."

She tilted her head do the side, looked him up and down, and then asked carefully, "Castle, have...did you hit your head recently?"

He let out a breathy half-chuckle. Gesturing towards the photo album laying between them, he asked. "If I was crazy from a recent injury, how would I have the photos?"

She gazed down at the book as though it might be covered in vipers. "I...don't know yet."

He hummed, knowing that she needed more proof before she would believe. "Then how about this?" He carefully flipped through all the photograph pages in the album to the paperwork tucked into the back. One was a faded, stained parchment from the mid-eighteen-hundreds. He'd preserved it as best he could and only pulled it out when absolutely necessary. Unfolding it with delicate fingers, he held out the sheet that listed out names, birth dates, and dates of death.

"What's this?"

"A list of our children. I can show it to you in family-tree form if you'd like."

Her eyes flared wide. "Ch-children. We have this many children!?"

He smiled at her shock. "Yes; twelve so far. Would you like to see more pictures? Hang on."

Castle moved over to the bookshelf where beneath a stack of books there sat a black, non-descript photo box. He lifted it, brushed some dust off the top with the palm of his hand, and then carried it back to Kate. He popped off the lid and showed her the organized rows inside. Each was grouped by year; that box in particular dating from the early 1900's through the 1970's.

"Wha…I…bu…" Kate merely stammered out unintelligible noises when she pulled out a photo of herself—well, a woman that strongly resembled her—wearing a navy-blue dress. The woman in the photo was crouched down on a lawn with each arm around a child: one a boy of about seven and the other a girl around four. The bottom corner of the photo had the printed date: 1951.

"It's a lot to process; I know." He had lived through all of it and there were some days when his brain could barely process it all. Then again, with nearly two hundred and fifty years of knowledge inside, it was understandable that available memory room was in very limited supply.

After gazing at a few more equally shocking pictures, Kate looked over at him and said in barely above a whisper, "How is this possible?"

He nodded slowly. "Ah, I must confess that is one question I am not entirely able to answer, because I don't know. Decades of searching haven't yielded me too much information. I have some research you're more than welcome to look at, but something tells me you'd be more interested to hear about all this," he said, gesturing towards the photo box.

"I…so…" She paused to place the box down on the desk. "So you and I—we find each other. We get married, have children, and then I die, but you don't. And…and the kids—they die too?"

He picked up the page with all their names once more and explained, "Well, yes, but no—they live out their natural life cycle as does everyone, but they're not all gone." He tapped his finger against the very bottom of the list. "Hannah is still alive; would you like to meet her?"

She appeared startled and took a step back from him. "Well, um, I'm not…I…oh! Alexis—what…how…"

Castle shook his head and gave her a brief half smile. "Oh, yes. That…she's another story." And certainly the first time he had to add such an explanation into his regular speech. "Everything you already know is one hundred percent the truth: Meredith and I were together, she got pregnant, and we had Alexis. She is, however, the only child I've ever had that isn't yours."

"Why? How?"

He shook his head. "Another long story I'm afraid."

Kate's brow acquired more wrinkles as she stared up at him. "Okay, so…Martha? If she's not your mother then how—Hannah; she's Hannah."

He bobbed his confirmation of her deduction. "Yes."

"O-oh. Oh. I…I need to sit."

Seeing her begin to sway on the spot, Castle stepped forward and cupped one hand beneath her elbow. He aided in her travel to the couch, and then quickly spun around for the food and drink he'd abandoned on the desk. "Here, do you want some coffee? Or maybe just water?"

She gazed up at him. "How 'bout whisky?"

"Really?"

"No."

"Okay."

"I just...I…" She gazed over towards the desk where the photographs had been abandoned and visibly shivered. "I… why didn't you tell me? When we met."

"When we first met? Because you would have had me institutionalized!"

"But I…well, I…I need to think a few minutes."

"How about this? You go have your coffee and eat something—perhaps the cinnamon roll? Meanwhile, I'll organize these pictures by time period and get ready to tell you our story, okay?" Though it was the sixth time around, Castle still felt the same excitement. Yes, Kate was stunned now—and she had every right to be!—but soon she would understand. He would help her understand and, as he did, he would get to watch the awe blossom across her face; that was always his favorite part.

Though it took her a moment, he eventually was able to pull her off the couch, hand her the coffee and pastries, and then send her off towards the kitchen. Then, turning back to his desk, he set to work laying out the story of himself, many Katherines, and their undying love for one another.

Prompt (from ladyalways47 on twitter, but originally a tumblr post from user shmurdapunk)

"imagine dating an immortal and finding a photo album of their exes who all sort of look like you dating back a century"

A/N: Hope you guys enjoyed the set up. The 2nd part is absurdly long because I couldn't figure out how to cut it up - it will be posted on Saturday