Hmm... Christmas Eve, and me with nothing to do...
How about an Omake~?
*creak*
Eleven year old Shirou's eyes opened in the darkness and he turned, squinting at the shadowed clock on the wall.
Just past midnight. Christmas Eve had become Christmas Day.
*creak*
The sound of wood shifting slightly made him blink, coming fully awake. An Intruder?
Mama wouldn't be awake right now, so did that mean that someone was trying to sneak into their house?
Did that mean...
Santa Claus?!
Quickly and quietly as he could, Shirou rolled out of bed and crept towards the door on tiptoes. The noise was coming from the living room, a steady creak of someone moving back and forth, then a rustling...
He hurried to the corner, eyes wide with wonder-!
And then his face fell, one part disappointment, one part confusion.
"Mama?"
"Eh?" The figure whirled, "What are you talking about? I'm obviously Santa Claus, and you're not supposed to see me. Go back to bed little one."
The woman Shirou saw had exchanged her typical blues and whites for a very short black dress and boots along with a black santa hat atop her head but there was no doubt that this was Arturia, her voice even sounded the same! Even if it was a little harsh, and her eyes looked a little funny, but that was definitely his mother!
Shirou's brow furrowed. "Mama what are you doing? It's late."
"I told you, I'm not your mother. I'm Santa Claus, spreading gifts and good cheer to all the good little girls and boys." In the mouth of another the words might have been spoken cheerfully but from her they were a near deadpan. "Hmm... Come to think of it, have you been a good little boy? Good little boys don't sneak around their house out of bed on Christmas Eve you know..."
Shirou for his part... Pouted. "Mama is being silly."
Yellow eyes rolled as she sighed. "Alright yes... Maybe your mother is being silly, but you need to go back to bed and let Santa finish delivering her presents."
The woman turned back to her bag and Shirou's brow furrowed even further. On one hand, he prided himself on being a good child, but on the other, he was curious as all children are. What was his present going to be?
Innocently, he cocked his head. "Did Santa bring anything for me?"
"Hm? Ah... Well I suppose, even if you're a nosy little boy you're not combative like those other children I delivered presents to... Let me see here... You'd like some friends right?"
Shirou nodded, he wasn't bullied or anything, but students tended to say away from him at school. Between the strange bright orange hair, his european mother with her strange surname, his survival from the fire, and the fact that he was rather quiet to begin with meant that no one had really gone out of their way to make friends with him. He wondered how Mama could do that though, and even Santa seemed a bit perplexed.
Which was when Arturia's voice came from behind him as she poked her head through the living room door. "Shirou? What are you doing u-..."
'Santa' froze, Arturia froze, and Shirou looked between them. Identical but for outfits and eyes. Then in a very small voice whispered. "Two Mamas?"
And then all hell broke loose.
"Shirou get back!" At the whipcrack command Shirou jumped away instinctively, clearing a path as Arturia charged, the dim moonlight peeling back from the blazing light as her sword and armor coalesced from air, lashing out only to meet a blade of black etched in crimson as 'Santa' parried! The winds howled in the living room as shockwaves of strikes battered the surroundings but Santa was fighting defensively, using the sack she carried in one hand as much as the sword she carried in the other.
"Damnit! I was just-! I'm just trying-!" The Black blade blazed and 'Santa' counterattacked, a mighty single blow that forced Arturia back for a moment. Within seconds she was charging back in, but those seconds were all she needed. "I can't deliver a present like this, but I'll do what I can! You'll see!"
Then she charged, not at Arturia but to one side, fleeing out the doors and into the freezing night, leaping into the air-!
And then vanishing as though yanked away, leaving only the faint sound of jingling bells in her wake...
Shirou -quite sensibly- passed out.
Apart from what Shirou and Arturia would both later agree must have been nothing more than a very strange dream (Some new dents in the living room furniture notwithstanding) the rest of the Christmas break passed quietly, but on the first day of classes the teacher had an announcement to make. A new transfer student for the new year, a girl with teal hair and slightly strange eyes.
When she introduced herself however the class consensus was immediate. Pretty or not, she was clearly Chunni.
Shirou thought nothing of it until she approached him during their break with a smile. "You're Einzbern Shirou-kun right? I was told to pass a message on to you from some strange Santa in a black miniskirt." She cleared her throat as Shirou froze. "Never let it be said that I don't deliver, even if this one is a little late. Merry Christmas Shirou."
Then the girl smiled. "I introduced myself earlier but I should do it again. My name is Kiyohime. I'm sure we'll be the best of friends!"
Somewhere in Fuyuki, Arturia felt a shuddering premonition of terrible things ahead...
This was utter crack churned out on christmas eve on a spur of the moment ridiculous idea. Don't think too hard about anything depicted herein.
For those unfamiliar 'Santa Alter' is a version of Arturia's 'Saber Alter' form from the christmas event in Fate/Grand Order. This idea came to me mostly because the notion of Invert!Shirou running into Santa Alter and immediately deciding that Santa can't be real because that is clearly his mother standing there was too funny for me to pass up.
The notion of her giving him kiyohime as a friend was just icing on the bizarre cake when all was said and done.
None of this is or will ever be Canon, just so we're clear. This is nothing more than me indulging in silliness.
Merry Christmas Everyone!