Disclaimer: I do not own Fate/Stay Night. Type-Moon and Nasu does.
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Okay, people, allow me to explain this logically impossible, crack-induced brain-fart I had. Back in the What if Shirou was raised by...? forum, I came up with a ridiculous idea in my head: What if a HF True End Sakura and Shirou had raised a shota-Shirou? Yes, I am fully aware that it is an impossibility on a cosmic scale. F*** physics. These are one-shots--they're supposed to be implausible.
To create some semblance of how the hell this comes about, allow me to formulate a plot setting (aka, make s#!% up). Basically, while Rin was messing around with trying to recreate the Jewel Sword, and had fiddled with the Kaleidostick at the time, she accidentally opened up a door to another dimension--and Shirou and Sakura were sucked into it. Thankfully, they were able to come back moments later... only to have an eight-year-old version of Shirou along with them, with no memories.
Sakura, ever the opportunist, decides to adopt him. Eventually, despite his awkwardness, Shirou accepts. And, thus, we are here, two years after F/SN, with papa-Shirou, shouta-Shirou, and Sakura-mama all living with Aunties Rin and Rider. And Taiga.
You can imagine where this will lead to...
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The young man awoke to the sounds of birds chirping.
Slowly opening his eyes, Shirou silently yawned to himself, stretching out his arms as he lay down. As he did, his hand brushed up against a familiar, warm presence. Smiling, he shifted his view to his side, gazing at the girl sleeping peacefully next to him.
Sakura, his lover and soon-to-be wife, had a small smile on her face as she slept peacefully next to him, laying on her side so she faced him. It had been two years since the end of the Grail War, and the two of them had to go through a lot to get where they were now. But to see her smiling, was more than worth the blood, sweat, and tears shed to get there. He moved to wrap his arms around her, perhaps to see if they could do a little... catching up.
Only to encounter some resistance; some invisible barrier, as he closed in towards her. For a moment, he was confused and frustrated at the development, only for realization to hit him, as he rolled his eyes, peering down between them.
There, an eight-year-old carbon copy of himself was latched onto her, his arms around her as he was resting his head in her ample chest, while she gingerly held him in her arms.
Lucky little shrimp. Shirou groaned mentally, irritated. He found himself increasingly disgruntled by Sakura's attention being recently stolen from him for the shouta version of himself. Ever since they had been salvaged from Rin's haywire spell along with him, Sakura seemed to never get enough of him. She'd pamper him with affection and attention, as any doting mother would her own child. Granted, Shirou did agree to let her adopt him, but he honestly felt irritated of her showering him with affection.
He wondered if this was how Archer felt when he interacted with him.
Sighing, he knew trying to pry the boy off her would be pointless. Still, he thought to himself, he might as well enjoy watching Sakura's peaceful expression...
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"So, you have to leave out early again tonight?" Shirou asked Sakura as breakfast was being eaten. Rider, Rin, and Shouta-Shirou were all eating alongside them.
"Yes, unfortunately." Sakura said with a sigh. "Nee-san hasn't been fully transferred back yet, and until then, I'm still in charge of this town. It's my responsibility."
"Well, I guess it can't be helped." Shirou said as he sipped his tea.
"Aw, do you have to leave, Mama?" Shouta-Shirou said with an innocent look in his eyes.
Sakura, for the umpteenth time that day, had to restrain the urge to glomp him to death. Nodding, she said, "Yes, Mama has a very important job to do for her Nee-san."
"Rin obaa-chan, why can't you do it?" Shouta-Shirou asked the raven-haired girl, who nearly broke her tea glass as she squeezed a little too tightly.
Giving the boy an evil look, she replied, "Chibi-Shi, didn't I say not to call me that...?" Everyone in the room felt a little scared by the Cheshire cat smile she gave, with the exception of Shouta-Shirou, who was blissfully unaware she was preparing to throttle him.
Laughing nervously, Shirou replied, "Rin, he's just a kid, don't be too hard on him..."
"...It's not fair." Shouta-Shirou said with a glum look on his face. "Mama is always so busy with work, and I don't get to see her much until bedtime."
The adults all shared looks with each other a little guiltily, the boy had to endure the absence of his mother because of a duty Rin was forced to leave her with.
"It'll get better soon, Shirou-chan." Came Rider's gentle voice as she petted Shouta-Shirou's head. "Just be patient."
The boy made a pouting face, looking at his food.
"Well, Mama won't have to leave until later tonight, so I can stay to have a bath, at least." Sakura commented with a smile towards her son.
The boy's mood instantly improved, a bright smile on his face. Rin and Rider had a difficult time trying to hide the rush of color to their cheeks. Sakura, meanwhile, nearly suffered a nosebleed.
"Which, of course, means Papa will be with her." Papa-Shirou said resolutely. The boy glared at his older self with obvious animosity, and the older gave him an annoyed look. Rin and Rider could swear they saw bolts of electricity passing between them--they were both vying for Sakura's attention.
"It's almost like it's..." Rin commented with a groan,
"Archer and Shirou." Rider finished.
"Well, I'm afraid Mama only has time for one bath, so you'll have to decide between the two of you." Sakura said with a smile.
"Alright!" "I'll win!" The two Shirous said simultaneously with an overabundance of enthusiasm in their tone. Immediately, they shot their hands out across the tables against each other.
"Rock, paper, scissors!!" The two said, shooting down their arms. Papa-Shirou had rock. Shouta-Shirou had paper.
The older Shirou fell to the ground on his hands and knees, a despairing look of defeat on his face, while the younger Shirou jumped in the air, cheering at yet another victory over his 'Papa'.
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"Um, Semp--I mean... Shirou?" Sakura asked somewhat shyly as he was about to head out for work.
"Hm?" Shirou blinked, turning towards her. "What is it, Sakura?"
"Er... are you mad at me?" She asked, holding her hands together.
"Why would I be mad?"
"Well, you've been acting somewhat grumpy ever since little Shirou came, and... I think I've been ignoring you because I've been pampering him. I'm sorry about that..." She said, looking somewhat guiltily at him.
Sighing, Shirou came up to her, hugging her firmly, surprising the girl. "Well..." He muttered, somewhat embarrassed, "I will admit I'm jealous of him. He has such an awesome Mama. I guess I just wanted to keep you all to myself. And letting him around you is somewhat nerve-racking for me."
The girl looked up at him, smiling. "Shirou, he could never replace you. Even if he is you, the man I love is the man right in front of me."
The comment made Shirou blush beet red. Shaking it off, he gave her a longing look--one which she readily returned--as the two closed their eyes, closing the distance between them as the leaned in to--
"Mama! Papa! I'm ready!" Came Shouta-Shirou running down the hall towards the door, in his school uniform.
Shirou and Sakura hastily tried to separate themselves, a blush apparent on both their faces.
"Mama, what were you doing with Papa?" Shouta-Shirou asked curiously.
"Oh, nothing." Papa-Shirou commented with a grin. "Just telling how much we love each other."
"Bleh!" The boy said, sticking out his tongue in disgust. "Ew!"
"C’mon, short stuff, we'll be late. Say bye-bye to Mama." Shirou said as he headed out the door.
"Okay!" Shouta-Shirou nodded as he ran up to Sakura, hugging her as she leaned down to embrace him. "Bye-bye, Mama!"
Sakura's head shot back, a torrent of blood shooting out from her nose at Shouta-Shirous weapon-grade cuteness.
"Oh, now look what you've done!!" Shirou exclaimed.
Recovering from her cuteness overload, she pecked him on the forehead, replying, "Have a safe trip, sweety." Standing up, she walked over to Shirou, kissing him on the cheek.
Older Shirou was having a hard time hiding his pleasure, as younger Shirou voiced his displeasure.
"Have a safe trip... Darling." Sakura said gently to him, a warm smile on her face.
Shirou nodded, smiling sweetly as he kissed his beloved Sakura on the cheek, producing a loving fluster on her face. "We'll be heading off."