For Emiya Shiro...
There's one reason for him to keep on living.
His baby adoptive sister Himeko.
Because in the fire, out of the people he could not save from the flames, she, the baby, was the only one he could save and protect until he himself broke down, but he kept shielding her with his body. Next thing he knew, they are adopted by the man who found them, Emiya Kiritsugu.
He adopted them both because he would not let the baby go, according to the doctors.
When asked way, he told the adults, 'She was the only one I could save. Everyone else melted in front of my eyes and after that, its my turn to melt like they did...I thought we're both gonna die and melt together too when I couldn't stay awake anymore. I thought...the baby shouldn't die alone so I thought I should die with her so she's not lonely.'
The doctors were visibly disturbed by his words.
They blamed his broken words on the trauma of the fire, and how people burned to death in front of him he described as 'melting' somehow. Both kids were lucky where hundreds had no such luck.
Their savior offered to adopt them both. Since the boy lost his memories, Emiya Kiritsugu named them both. He is Shiro, and the girl is Himeko.
See, their new father is a Magus, a person who can do magic.
'You can do magic, jii-san?' Shiro asked Kiritsugu in amazement.
'Yeah. When I found you and your sister, she too, is magical because when I found you, a barrier coming from her was protecting you from the flames.' said Kiritsugu with a fond smile. 'You two are destined to meet.'
'Can I do magic too?'
'You can but the path of a magic user is perilous. To have magic is to walk with death every day.' said Kiritsugu with a sad smile.
'Teach me jiisan! That way I can protect Himeko until I can teach her someday!' Shiro piped up.
'Its hard work and painful! You sure?'
'I'm sure! I'm gonna protect Himeko until she gets married someday!' Shiro chimed in determination.
For Kiritsugu, that was at least, a reasonable reason and its dedication when he saw one and thus, fate changed for his entire existence as a result.
'Alright. But I'm very strict.' Kiritsugu warned him good-naturedly.
And so, Kiritsugu started their lessons together with Magic Circuits...after removing Avalon from Shiro once he fully-healed as Kiritsugu abandoned his idea of crushing Shiro's hopes by leaving it inside him, effectively changing his Origin and Element that would make him an inept magus if the boy has stupid ideas. But since Shiro only wishes to protect Himeko, the only one he could save, he took it off before Avalon began doing the damage he intended.
'You're lucky you're a kid because its easier to start training as a kid.' Kiritsugu told him. 'I'm guessing you're around 6-7-ish, ages Magi start training.' he said. 'You have 27 Circuits which is fairly good for a human who just gained some. But when humans awaken to Magic Circuits, its usually very few in number and of feeble quality yet you have a very average number and average quality you're lucky. Himeko on the other hand seems to be from a very old bloodline because her numbers and quality are high. She has 80 Magic Circuits of A-Class, meaning, her family must be around for more than 500 centuries.' Kiritsugu noted. 'A Magus Lineage practices Blood Thickening by marrying partners with high amount of circuits so that the child born would have plenty, but always one circuit more than the parents. Makes me wonder who Himeko is but nobody came forward to find and claim her from us.'
And so, for five years, Kiritsugu trained Shiro every after school as during the day, Shiro can train his magic circuits while Kiritsugu is on the lookout for the Tohsakas and the Matous.
The Emiyas got information that Tohsaka Rin is orphaned, Tohsaka Sakura is adopted into the Matou as the Matou child has no circuits and Zouken went missing. So now the family head, is Matou Byakuya. Tohsaka Rin is under the Guardianship of his most dangerous rival, Kotomine Kirei and Kiritsugu pitied the girl, thinking she'll grow up as twisted as her guardian is.
Then again, he's no better, but at least, he tries hard to be a good father to his new fledglings. He wasn't a good magus as being a good magus means exposing children to cruelty at a young age by cruel upbringing as a magus. So he just taught Shiro spells. Spells he knew that made him who he is as the Magus Killer. But when he was ten, old enough to be left alone, Kiritsugu would go on trips, ordering Shiro to do physical training while he's gone as Magi should also be strong in body to last long in fights. Himeko is now three years old, can walk and her ability to talk is limited as expected for a child her age...and she started training after their fifth New Year's Eve as a family.
But Kiritsugu started to get dangerously ill a year after...and by the time Shiro is twelve and Himeko five-and-half, he passed away, orphaning both kids twice, leaving them his fortune and belongings, and their house, further motivating Shiro to be a good family man as Himeko's only family left. He got more overprotective than ever with a good reason.
Kiritsugu told him all about Magi.
And Himeko has great potential yet the two foster siblings have no powerful guardian to protect them, and there's two families in Fuyuki. The Tohsaka and the Matou. So she will NOT start Kindergarten and is to be home-tutored by the Fujimuras while she trains her Magic Circuits at the same time. The only time she'll start going to grade school is when she's 7 wherein by then, her circuits are almost done in training she can practice basic spells now. At an age when she is now somebody's 'claimed apprentice' so she would be safe and 'hands-off'.
Shiro also did some research.
His sister possessed a Bounded Field cast by someone Kiritsugu presumed was family. A strange field that doesn't allow anything it considers 'bad' to even get close to her. He once held one of his precious bullets above her and dropped it on her, and the bullet bounced away off an invisible force. However someone or something more powerful can shatter it and they would rather not chance that. And the barrier once extended to Shiro in the hellish flames years ago. Kiritsugu never figured it out how it works, so he gave up and would rather focus on 'what can be done' not on 'what they can't do'. Himeko's element was Wind, while he was Earth.
He researched on what they can and can't do. But Kiritsugu would say, 'We live in modern times while the arrogant magi doesn't even know what a TV or a radio is. Think modern Shiro. I used guns more than my magic. Being modern and up-to-date with the times saved my life more times than tradition did. It will help you and your sister live longer for sure.' since Shiro cannot use firearms, he focused on martial arts, fencing, and later, archery while basing his magic based on his abilities, and making home life more luxurious than it seems. For Himeko whose body is still frail and still training, she favors the traditional way of shooting spells while running around in evasive maneuvers and being elementally-wind, she could do many things she could think of, based on knowledge off of comic books of all things. But hey, it helps. Why would Shiro complain?
The things the siblings have in common that the Fujimuras noted is that they are very close to each other more than how close actual blood siblings are in most families, and highly protective/defensive of one another. Both siblings are also incredibly good cooks and good with chores that Fujimura Taiga is only their legal guardian on paper when they're perfectly capable of taking care of themselves. That, and Himeko is taken home by either Shiro or Raiga's subordinates, as she learns martial arts with the other yakuza until Shiro comes home from club with his friend Sakura. She began coming over in Middle School and she's from the Matou House. However, Sakura wasn't a practicing magus despite her well-trained circuits. Her body is soft and frail making them wonder what the hell were the Matous thinking, wasting her potential but at least she was no threat to them. But come when Sakura was 14, she quit school for a year because she got severely sick.
After that, she could no longer come home with her father who always takes her home.
Shiro figured that since she got sick, her family is a bit stricter.
But Himeko didn't care because their house is theirs again.
They lived a pretty isolated life. Sure they have friends in school, but Sakura was the only 'friend' allowed in the house.
Because she and her brother are Magi. Her brother being the more-seasoned one while she, in training.
How can they practice with people in the way? When Taiga was over, all they could do was train their Circuits and martial arts after cooking dinner because for two hours afterward, she watches TV while eating homemade senbei crackers before leaving.
'Nee nee oniichan,' Himeko asked one day around January. 'When will Taiga stop coming over~its hard to train in magic when she's around in weekdays.' she complained. 'Can't we do something?'
'As much as I want to, its her job because grandpa asks if she did her job.' Shiro sighed as in the backyard, they're training their magic spells and techniques. 'That, and we're apparently preparation training for her future responsibilities as a wife.'
'What responsibilities?' Himeko drawled, dripping her question in thick sarcasm with an expression to match. 'Who does the chores and cooking while she watches TV while snacking?'
'Well...grandpa doesn't know that.' Shiro snickered. 'Oh well, he'll know the truth years later and we can say karma bites back.'
'Hmph, I suppose so.' Himeko snorted. 'But its still annoying. Progress is slower at this rate.' Shiro inwardly rolled his eyes and mussed up her hair.
Between them both, while he was the protective doting brother who lets things happen naturally, she was the serious one, more worried about their training as Magi because of 'time wasted'. While school is a necessary time spending to her, having to waste two hours in waiting for their guardian to leave when a lot could have been done in those two hours. Such as more percentage increases in mastering a spell or technique! So yes, she wasn't too happy with Taiga around when at 17, Shiro could have fully-mastered his abilities by now and become a fully-realized magus, master of his abilities. but alas, Taiga wastes their time that Shiro would be a fully-fledged magus by the time he graduates college and that's way late so yes, little sister is one unhappy camper.
That, and she is worried for their future as civilian magic users. Sure they want nothing to do with Magi but they wanted to be the best they can be incase they encounter no-good magi.
Magi who would be after her for her potential if they scan her.
If not as an experiment in their lab which is a BAD THING, as a wife for their son which depends...and Shiro took to learning the art of being a Magus Killer to protect her from such louts so she studied magic to aid and support him but she's no slouch as a fighter either.
She's not training with the yakuza for nothing!
That, while Shiro is the doting overprotective sis-con...the kind who is her mentor and protector and paranoid of their surroundings...
She's a bro-con...with dangerous feelings to match.
For her, since their father's death, Shiro is her whole world since he gave her everything(nothing materialistic but his time, familial love and affection) that in turn she does the same. Even cuddling with him on the couch on their off-times while watching TV together.
For the girl, nothing else matters.
Everyone around them are normal humans, and their fellow magic users dangerous to them. They're isolated and all alone.
But one day...
Their life changed...and not in a good way...