Here you go, Takeshi Yamato. I hope this fits most of the requirements you set for a Nanoha/KH story. Hopefully the muse will get a firm kick in the rear for it!
The Keyblade War. A time when men and women fought over the true "Χ-Blade", only to for it to be scattered beyond recognition in the end. In the wake of the Keyblade War, a new order dedicated to protecting Kingdom Hearts was formed. The members of this elite group were Keyblade Wielders who chose to defend the light, rather than use it for their own selfish purposes.
Time has passed, and a new Master has been chosen from the remnants.
However, her quest takes her to a place that will change the destiny of the realms, in more ways than one...
She can still remember that fateful day. She had been walking home with her mother when they stopped for an ice cream. One moment she was standing with her mother, the next she felt herself snatched by a strange man with a terrifying grin.
She started crying loudly as she wanted to go back to her mother, but she got slapped for it.
Then she felt herself falling a few inches before warm hands caught her. She looked up at a woman with kind blue eyes and light blue hair. She looked angry at the man, and had a strange weapon in her hands.
She didn't really remember what happened next, but found out later that the man was someone who targeted young children like herself and was sent to prison where he was less than welcome by the general populace.
Even criminals have standards, and they generally disliked creeps who targeted young girls.
Nanoha would never forget the woman who saved her life.
Aqua. She had no last name, and her clothes were a little...odd... but the one thing she remembered the most was the weapon in her hands. It disappeared the moment the authorities arrived.
She would see her one final time before she vanished to wherever she came from. Aqua bent down and handed her a different blade to the one she had before.
"This blade is called Rainfell. It has served me for many years, and I just know you can put it to good use when you're older. Follow the Light, little one," she told her, before patting Nanoha on the head.
And like that, Aqua vanished.
Ten years later...
Nanoha blinked at the sunlight and withheld a groan. Yet another boring day.
Ever since she was almost taken by a pedophile, she had been stuck taking lessons with her siblings. It wasn't that she hated swords...she certainly didn't like the memory of being completely helpless when she was five and taken from her mother...but she didn't exactly enjoy waking up so early.
Though she was fairly certain it was the look in that creep's eyes that turned her off men. At fifteen, Takamachi Nanoha was very well aware she preferred girls to boys, and thankfully her family and real friends accepted that choice.
Her mother's only request was that they get a surrogate or adopt so that she might have grandchildren.
Nanoha got ready for yet another day of her last year in middle school. She had always felt she was destined for more than just being a regular girl, but that had never panned out.
At least she didn't have to go to cram school anymore. Her grades were some of the highest in the class, especially math.
Sighing, Nanoha stared out the window wishing something, anything would happen.
She had no idea how complicated her life was about to become in just a few short hours...
A blond teen was running for his life. He had thought he could handle sealing the Jewel seeds. He was wrong. So very, very wrong.
Being a sensible person, rather than stick around to try again when his first five attempts failed spectacularly (to the point he was bleeding from a few injuries caused by the backlash) he was running like his life depended on it. Because it most certainly did.
The seeds weren't sentient, but they could still hold one major grudge.
A branch launched by the rather irate lost logia sent him sprawling into the ground. In a last ditch effort to save his life, he turned into his ferret form.
The seed flew past him, and he cowered hoping like hell that it didn't find him.
He let out a silent sigh of relief when he sensed it had disappeared. Mental, magical and physical exhaustion hit him like a brick. He had been trying to collect the seeds for two days straight with very little rest, and to make matters worse he was experiencing some magical backlash from the failed sealing.
He passed out, the odd red gem he discovered while in another set of ruins hanging off his neck like a collar. He had learned quickly that "Raging Heart" was very choosy about it's owners. It would let him use the base functions, but the higher ones were beyond his reach.
His telepathic plea was sent on a broad range of frequencies, and it bounced around until it hit something.
Nanoha paused on her way from the mall. She just wasn't feeling up to shopping today, despite her recently gained allowance. And any junk food she bought would inevitably come back to bite her during her sparring sessions with Kyouya, her brother.
She wasn't a prodigy, but she was still better than most girls her age. Then again, kendo was considered a boy's sport.
Nanoha grimaced at the memory of the tongue lashing her brother gave her when she overdid it with the training regimen after a particularly unpleasant encounter when she was nine. One of her friend's family had an unpleasant business associate who tried to kidnap Shizuka, and would have succeeded had it not been for Nanoha causing a big enough fuss with her rather rough attacks using a branch she found. She managed to fend him off long enough for the adults to arrive, but had nearly gotten shot in the process from a gun she wasn't aware the man had.
She had nearly trained herself to the bone to avoid being 'weak' again, as it had brought up memories of her near abduction.
Needless to say Kyouya wasn't too happy finding out she collapsed during gym class and the reason behind it. It had taken her an entire year before she could train on her own again, and even then her family kept an extra close eye on her because it was clear she needed someone to set the limits of what she was allowed to do.
She left the mall after saying by to her friends, deciding to take a walk around the park. She had a can of mace in her bag...a remnant of her almost being abducted ten years ago and a compromise seeing as how she wasn't allowed to carry her bokken to school except for kendo meetings. She wasn't even part of the school's kendo club, because she preferred the personal training her brother gave her and Miyuki.
It was because of this that she heard the plea for help. It took her the better part of two hours to find the ferret, and another to locate a vet that was open this late.
This was not how she planned to spend her bi-weekly allowance.
"A ferret?" said Shiro, her father.
"Is it tame?" asked her mother.
"It didn't bite the vet while she was prodding it, and it didn't freak when she picked it up either," said Nanoha.
"I suppose you could keep it... but you'll be responsible for taking care of it. I don't want to hear it got sicked because you forgot to feed it," said Momoka after considering it.
"Yes mom. The vet said I could pick it up in the morning. She wanted to keep it under observation for the night just in case," said Nanoha.
That and she needed Nanoha's parents to give permission before she released a potentially wild animal to the girl.
It was a good thing tomorrow was the weekend.
The next morning...
Nanoha came with her older brother Kyouya to pick up the ferret. While he lived with his wife, he still came to the dojo every day without fail to train his sisters. He had inherited it after the wedding, once their father deemed him ready for the responsibility.
The ferret didn't try to bite her once, though he looked a little nervous around her brother.
It wasn't until they had to deal with a strange intruder in the form of a blob monster that their lives were upended.
Nanoha wasn't panicking like most would. Instead she looked at the blob for weaknesses.
Whatever it was, it wasn't alive and that dispelled anything that would hold her back.
She didn't want to be a killer, and her father accepted that fact.
However seeing the blob nearly hurt her mother, Nanoha's passive personality shattered. She would not let this thing hurt her mother.
So she considered the "ferret's" offer carefully. The odd red jewel seemed to resonate with her, and for a brief moment she felt the sensation of falling.
Below her was a strange platform that looked like stained glass. It almost felt like a dream, but it was a bit too vivid, too real.
So you are the one who seeks to become my new Master. Well, you have spirit, more than the Ferret-Boy does. Let us see if your will and soul can handle the power you seek!
Nanoha found herself confronted with three choices. A sword that wouldn't have looked out of place in a mecha series, a white staff with a gold top and red jewel, and a magical shield that had a deep red jewel in the center.
Chose wisely, for there is no going back. Will you chose the valiant swords, relying on your skill and magical ability? Will you chose the stalwart staff, blasting your enemies from afar? Or will you chose the hardy shield, preferring defense to offense?
Nanoha didn't think twice about her choice. She reached for the staff and once her hand grasped the shaft of the weapon, she heard the voice again.
Are you sure?
She removed it from the pedestal. The stained glass crumbled from under her, revealing a new one. This one had a figure on it she recognized from her memories.
Once again, there were three pedestals, though one was empty.
Chose what you will give up. Close range skill or defense.
Again, she didn't hesitate. She was confident in her own skills from years of training with her brother, so she picked up the shield.
You wish to abandon the sword?
"I can train with my family. I don't need anymore help than that. But a defense against my own blasts would be nice," said Nanoha, mostly to herself.
It was always a good idea to have some proper defense when you planned to blow things up.
This time a set of stairs appeared. Nanoha found herself trying to fight monsters not too dissimilar to the one that had attacked... was still attacking her house.
She pushed aside any doubts or fear. It was nothing compared to the time she had nearly gotten killed protecting Shizuka.
Good. You'll need that courage for what lies ahead. For as the light grows, so does the shadow behind it.
Nanoha woke up in time to realize that she was forming a new barrier jacket. Thinking quickly, she formed something similar to what Aqua had worn the day she saved her. However around her was a cloak that almost looked like her old school outfit. In fact if she pulled it around her, it could have been mistaken for it.
In her hand was the same staff she had picked from that weird dream.
~Stand By Ready, Set Up.~
The voice was quite a bit less imposing, but she recognized it immediately. It was the same one that talked her through the strange trials.
The rest of the night passed by in a blur, but at the end of it there was one very nervous ferret-turned-boy in the remnants of the Takamachi living room and a surprisingly understanding family looking at the youngest daughter.
Nanoha had always felt like she was meant for more than just running the store, or being an accountant (mostly due to her way with numbers). Becoming a magical girl wasn't that far fetched.
"Well, I can't say I wouldn't have jumped at the chance at that age myself, and Nanoha is rather responsible...except when it comes to her own health. I'll allow it on the condition that she doesn't push herself or this...linker core...to the point she endangers her own health," said Shirou after considering it.
Nanoha perked up at that.
Yuuno Scrya, once he realized Nanoha had busted him as an animagus (whatever that was) to her parents, was given the spare bedroom while Shirou called in a few favors to get the house repaired...and the defenses upgraded.
Magic wasn't as unheard of as Yuuno might have thought, and the only reason why the home wasn't already defended was because they lived in a city, where such attacks were rare.
He did wonder why Nanoha was switched from a "bokken" to a spear-like weapon they called a naginata.
In the dark abyss, a figure twitched as it sensed the awakening of a new Keyblade wielder. But this one felt different...and familiar. For one thing the keyblade felt off, for lack of a better word.
Far away in another world, a girl with wine-red eyes looked up from where she was reading. She felt the winds of destiny shift slightly. Not enough to irreparably change her own path, but enough that a few tweaks were made.
Fate hid the wince as her wounds cracked open, and her familiar looked at her worriedly. Aruf came in and changed the bandages with practiced ease. Her strange healing spell was good, but there was a point when even Cure couldn't handle the damage done by that woman.
After she found out about her older/younger sister Alicia, and realizing she was nothing more than a replacement that her mother discarded of the girl, something had snapped in Fate. However she found the files about Project: Fate, she had high doubts the TSAB would help her. After all, they would just use her to get to Precia, and despite everything done to her, she still loved the woman.
That didn't mean she was still a mindless drone though. If she found an out, she was going to take it, loyalty be damned. Aruf hated her 'mother' more than her Master did.
Like Fate, she'd jump at the chance to get out of this nightmare they were stuck in.