This is a Chrono Crusade/FSN cross, with limited interaction from Chrono Crusade.
The fire. It was the first thing he could remember as "Shirou Emiya", for that was when he first saw the smile that would change his world.
Kiritsugu adopted him, never knowing that he had saved a fellow Magus.
So imagine his surprise when a known Magus lawyer from Germany (he was often hired by the von Einzbern, enough said) showed up at his doorstep.
Mr. Acker looked at Kiritsugu with some amusement, and immediately said "I'm not here representing your wife's family today. Rather I'm here representing your new son's birth family, who were eager to find him."
"Come in," said Kiritsugu, after a moment. Acker didn't care much about the Root or even about other Magi. He got paid enough to represent them in the Magus Association when ruining another family financially or pleading the case of a favored member was easier. But his fees were expensive to those he didn't like.
Kiritsugu had always gotten along with him, because Acker was a no-nonsense Magus who didn't put up with the bullshit of others. Acker made quite a mint settling estate disputes whenever Kiritsugu finished a job, so they got along a little too well.
Shirou was currently with the Fujimura clan's granddaughter, buying groceries. It also doubled as a Japanese lesson, since the amnesia apparently extended to Shirou's memory of languages for some odd reason.
He had a passable knowledge of English, and he could barely comprehend Japanese.
"So why didn't you show up sooner?"
"The family only received word that a red-haired child matching the heir's description was seen at an area hospital. They had come here to broker a marriage contract with the Tohsaka family when the fire broke out."
There was only one family that would bother to broker a contract with the Tohsaka, considering how 'young' they were. Not to mention the fact that they were only noteworthy in that Zelretch threw them a bone once and they helped to create the Grail Wars by volunteering their family lands.
"Shirou is from the Harvenheit family?!"
"The heir, in fact. He showed a particular knack for the family's Jewel Summoning art, more so than any of the other members. He's scheduled to have his family Crest added to him when he turns fifteen, or when he finishes basic Magus trials."
"I take it some of the family doesn't want him to claim the crest?"
"To put it mildly. Some of them tried to hire me to kill him if found alive."
Kiritsugu snorted. The more things changed, the more they stayed the same.
"However if you were to name him your son and give him what's left of the Emiya crest, then they'll have no reason to come after him."
"That explains why he can't speak Japanese very well," sighed Kiritsugu. "If I were to train Shirou until he reached the standard required, could he still obtain the crest?"
"He would have only one chance. Each heir has to prove themselves worthy of the honor to be head of the family, and they only get one shot. If he fails, then it defaults back to the previous heir."
"Sensible," said Kiritsugu.
Acker brought out what looked like some sort of odd diamond on a simple necklace.
"This is what they use to test the worthiness of the heir. When he's ready to try his luck, tell him to put some of his blood on the gem. If it accepts him as head of the family, then he'll know pretty fast. If not, he'll just get the safety deposit box with the standard amount of jewels and some of the research left by his parents. Here's the key to it, as well as the address in Fuyuki."
Kiritsugu took the gem and the key.
"If he's not the heir, then what?"
"Then you call me and I'll return the testing gem to the family, no questions asked. The only thing that will happen is that he'll become head of the Emiya clan instead."
Who knew, maybe Kiritsugu could use this as a chance to reclaim Illyasviel from the von Einzbern family.
"Now, are there any questions?"
"I'll call you if anything comes up."
With the knowledge of which family Shirou actually came from, and a basic idea of what he could do, Kiritsugu decided to try another tactic when training him.
He was going to try and bring the "Magus" Shirou out, since his current self could only use reinforcement and structural analysis.
So Kiritsugu did something he would normally laugh off as 'nonsense'.
He put Shirou under hypnosis, in the hopes that his 'former' self was still in there somewhere, simply buried.
Much to his surprise (and relief) he lucked out. The Harvenheit side of his son was still very much alive, just stuck in Shirou's subconscious. The only problem?
He couldn't remember his own name. Oh, he remembered which family he came from, and the lessons he had taken to learn Jewel Summoning (which was the family's proudest contribution to magecraft), but small things like his full name escaped him.
So Kiritsugu decided to give him the chance to come up with a new name for himself.
The name Shirou's original self chose?
Säbel Harvenheit Emiya.
Mostly because Säbel knew what "Shirou's" element and origin were...and they weren't exactly good for learning normal magic.
Shirou was a "Sword". Säbel was a "Jewel" with access to all five of the standard elements. Hence why Säbel was considered the heir...he could use most of the Jewel Summons with an efficacy that the previous heir couldn't.
Which meant Kiritsugu would have to alter his lesson plan for "Shirou", while teaching Säbel everything he knew about magecraft.
Mostly because Säbel agreed that if he found Illya he would do everything in his power to get her away from the von Einzbern clan.
The Harvenheit clan was just below the Einzbern, so naturally they had something of a 'rivalry', despite the fact they were slightly smaller in number.
And getting one over the Einzbern by taking the next "Lesser Grail" from them would naturally appeal to the Harvenheit family. So much so that they agreed to send tutors in the event something happened to Kiritsugu.
Six years after the Fourth Grail Wars end...
Kiritsugu's death was a hard blow for Shirou, even if he died rather peacefully. Sadly Shirou couldn't help but feel as though he was partially responsible for his father dying early.
Three months before he died, Kiritsugu gave Shirou what little remained of the Emiya crest. Shirou was now the dubious 'head' of the Emiya clan, which only had only one or two members...and almost no crest to speak of.
The most Shirou was able to do with his new 'family crest' was make it easier to carry around his magus equipment without any normal people noticing it. He simply used it to make a 'pocket' outside of time by a few seconds, which he could access by 'slowing' or 'speeding' the item he needed until it synced up with him.
It made carrying books around so much easier.
Shortly after, when Taiga's grandfather called the number Kiritsugu gave in the event he died, someone from Shirou's birth family came to teach him magecraft...though they had already been warned to 'hypnotize' him if they wanted teach Shirou anything and actually make progress. Shirou was good at runes, projection, reinforcement and he had the nose of a bloodhound when it came to magecraft.
Säbel was the prodigy at magecraft, and he took to the lessons far better than his 'surface' self did.
In terms of magic, Säbel was superior to Shirou. However in terms of personality, Shirou was liked more than Säbel was, because he was honestly nice.
Säbel preferred the term "hopelessly naïve, but not to the point of complete stupidity". Most people (mainly Taiga who ended up finding out about "Säbel" by accident) thought Shirou's other personality was a bit of a jerk, even if he was the better fighter of the two.
Taiga thought Säbel was an ass...even if the most Shirou could do about him was keep him from being an indiscriminate killer. You couldn't gloat about being the superior Magus if your opponent was dead after all.
Still, Shirou felt sad about his dad's death. He was the only one that really encouraged him to become a hero.
Even though Säbel thought it was a rather naïve dream.
Shirou decided to go on a walk and enjoy the sunset before he went home for a rather lonely night. He wasn't expecting to find a lawyer waiting for him.
"Guten Abend, Herr Harvenheit."
(Good evening, Mr. Harvenheit.)
"Good evening, Mr. Acker."
"Gomen, I forget you don't speak German as Shirou, Emiya-san."
"I take it this is about my dad?"
"Indeed. Kiritsugu-san made sure that you would not be lacking in instruction should his demise come before you had completed your basic Magus studies, so he asked me to act as a go-between with an up-and-coming teacher at Clock Tower. Lord El-Mellio agreed to be your teacher until you at least had the basics down, but if you want additional instruction you can work something out later."
Acker then pulled out a letter.
"This is your father's last will and testament, written right before he gave you the Emiya family crest. There is also a letter from Kiritsugu-san himself, for you and for one other."
"Who gets the other letter?"
"Kiritsugu's daughter, your step-sister Illyasviel von Einsbern."
"...I have a sister?"
"An older sister. She's the daughter of Kiritsugu and the previous Lesser Grail of the Grail Wars, Irisviel. Unfortunately all attempts to barter for her with the von Einzbern family have failed. Apparently Jubstacheit was very angry at the fact Kiritsugu ordered his Servant to destroy the Grail, rather than retrieve it like he had been ordered."
"Why do I have the feeling that's going to come back and haunt me later?"
"Most likely," agreed Acker. "Now about your training. You can chose to either attempt a claim towards the title as Heir and future head of the Harvenheit family at fifteen, or until you finish your studies. However, you must wait no later than your twentieth birthday to stake a claim. If proven worthy, you will automatically receive the noble phantasm of the family. The method of delivery was not disclosed to me, however the effect should be within five minutes."
"And if I don't prove worthy?"
"Then you still can claim to be a Harvenheit, but the most you'll get from the family is the safety deposit box left by your birth parents here in Fuyuki with the research materials of their branch and the standard arraignment of jewels to work with. There was also an undisclosed amount of money that can be converted to yen," said Ackers immediately. "This doesn't include the money Kiritsugu left for you."
That money was being managed by Taiga's grandfather until Shirou learned how to do it himself.
"There is also the matter of the contents of Kiritsugu's safety deposit box for you to examine after you've completed your training in the basics. Once I've confirmed you qualify as a proper Magus by the Association's standard, then I will hand the key to you as per his instructions."
"And what about that contract you told dad about when you first came here?" asked Shirou.
"That contract is considered on hold until we have the agreement of the head of the Tohsaka clan, as he failed to sign it shortly before his demise in the last war. Depending on whether the girl in question finds the contract and signs it after obtaining the Tohsaka crest, it may become void."
"So there's nothing I can do."
"Not legally, no. Kiritsugu never had a copy of the original contract, and the one in the hands of the Tohsaka clan went missing after the war."
Shirou didn't exactly like that, but there was nothing he could do. At least he wasn't potentially engaged to the Edelfelt clan...he'd heard things about the heiress. Terrifying things.
Waver Velvet El-Melloi wasn't entirely sure how he felt about being in Fuyuki again. Especially with a prospective student that was apparently close to the Magus Killer.
So imagine his surprise when he finally met this "Shirou Emiya" in person.
He was nothing like his adopted father, let alone any Magus Waver had to deal with considering who had hired him to teach the kid. The Harvenheit family were almost as snobbish as the Einzbern clan. Almost.
"So, how far along are you in your studies?" asked Waver, after eating a late lunch. It was better than any of his attempts.
"Oh, I'm not actually the one you're teaching. The most I've ever done was master reinforcement, projection and a decent amount of runes and ward schemes. Säbel is the one who needs the lessons."
"Who is Säbel?"
"Mr. Acker didn't warn you?"
"Warn me about what?"
"It's easier to show you than to explain. Let's just say there's a reason why I never got past projection and runes."
Shirou muttered something under his breath in German, and much to Waver's disbelief, there was a subtle shift in him. It was hard to put his finger on it exactly, but he went from an easygoing nice guy who wasn't exactly that good at traditional magecraft, to a highborn Magus.
It was when Shirou looked Waver in the eye that he knew that this wasn't the same person who had welcomed him into the home.
"What the heck?"
"Call me Säbel. It's easier that way."
Even his tone was different. Not to mention the clear German accent in his Japanese.
"And who is Säbel?"
"The original personality. Now buried under the hopelessly naïve Shirou Emiya. From what I understand, you were here for the last war, correct?"
"I left before it ended. I wasn't going to take another Servant after losing mine," said Waver.
"Do you recall the Fire that erupted at the end of it?"
"I heard about it. Wait, you're not saying?"
"The fire almost erased the original personality, which was barely saved by adding it as a subconscious 'secondary' one. As a result, Shirou is the day-to-day face, while Säbel is the 'Magus' oriented personality. As a side effect, I am better at Magecraft than Shirou, while Shirou is better at the everyday ordinary things like cooking."
"So that's why you need someone to train you."
"Shirou has an element and origin that limits his capability as a Magus. I have one that is almost perfectly suited to my family's brand of jewel magecraft, but no one to help me adjust it so I can stake my claim as heir. You were highly recommended since you had already been to Fuyuki before and knew how to speak Japanese."
Not to mention the fact that Waver was considered a "traditional" Master for the Grail War, which according to a recent study would start fifty years too early. Säbel needed to be trained now, before it restarted, if he wanted to insure that they didn't get killed off.
"So why did Shirou suddenly speak German?"
Säbel had an annoyed look on his face.
"Shirou was tired of being hypnotized, so he came up with a passphrase that was easy to remember in German to bring me out without help."
Waver nodded. That was a good idea.
"Shall we get started then? I'll need to know where you're at to see how long this might take," said Waver.
Good thing Säbel set up a 'temporary' workshop and warded it against Taiga.