Author Notes

Hey guys. Tuna's speaking (or gaping like a fish supposed to do). I've been wanting to write a fic ever since I enter the fanfiction world four years ago, and finally! :)

Though, English isn't my native language, and it's even more confusing that I'm writing a fic in which the story is taking place in Japan. I tried to be as resourceful as possible, but, well, you get what I mean. (I'm Indonesian, by the way.) SO! My dear friend SwitchbladeSunsets had agreed to be my beta! Really grateful to have her. :)

Oh! And I'm using FSN Heaven's Feel for this fic. Mind you, I haven't watched the movie (the Blue Ray version should come out on May, if I'm not wrong) nor have I read the novel yet, so I could only reference from Typemoon Wikia. If there are some discrepancies, please do PM me for it! I'll fix it as soon as possible.

I have a couple more things to say, but meh. Let's just start the story.

*Note: Edited on 27/3/'18 - Avalon

Edited on 16/4/'18 - Tsuna's current age (7 years old), Greater Grail, projected Excalibur and some cursing.

Disclaimer: I don't own KHR or Fate series.

Flames of Steel

Katekyō Hitman Reborn! x Fate/Stay Night: Heaven's Feel

Beta: SwitchbladeSunsets

It was the largest pool of blood Tsuna had ever seen. Granted, it was mixed with rain water, but still.

He wasn't sure if the pungent metallic scent of blood was the first thing that had caught his attention, or the river of red flowing down the pedestrian road as he trudged toward his house, or the particularly large flock of crows perching on one side of the electric wires. Or something else, like a gut feeling.

Tsuna didn't know why nobody else had ever noticed these signs. But here he was; his soaked shoes millimeters from the red flow.

The pitter patter of heavy rain drowned all sound, creating a tension-filled atmosphere. The sight was like a particularly morbid murder scene right out of a horror movie (or that was how he thought of it, the horror genre wasn't exactly meant for a scaredy-cat like him) but no matter how scared he was, how terrified Dame Tsuna was, he just couldn't look away.

It was a man, no, an older boy, slumped against the wall like a corpse (or maybe he was one). He seemed to be of Japanese descent, but his hair was a peculiar shade of red (or maybe it was actually blood, Tsuna didn't know and didn't want to know). The boy was… asleep. He sure looked really tired, Tsuna could tell from his eyebags. His left arm though looked quite disturbing. Unlike the rest of his pale skin, the arm was darker and more muscular, as if someone had attached it to his body like a F… f-frankens… something. With his tattered clothes clinging to his body, he might as well have been one.

The 7-years-old boy wanted to shriek in fright and horror, wanted to go back to his mom and beg to her to please, stop this nightmare, but before he could even inhale deeply he noticed a few short puffs of mist in front of the corpse's face.

H-he's alive? Tentatively, Tsuna reached out and placed his trembling palm on the teenager's chest. After a few moments, he could determine the periodic rise and fall of the chest, indicating that the boy was indeed alive despite all the bloodloss and the Franken-thingy qualities.

But before Tsuna could retract his hand, something in the deepest part of himself reached out towards the dying boy.

Unknown to Tsuna, his Sky Flames flowed into the boy's chest and towards the mismatched arm. Although stunted by the Ninth's seal applied just two days ago, his Sky Flames still retained a portion of its true potential. Its Harmony characteristic, which helped maintain a balanced state, identified the wrongness of the limb - though it technically came from the same person albeit from a different timeline - and sought to correct it.

The arm belonged to a spiritual body, a Heroic Spirit's, and its transplant to the boy's human body should have been impossible. Yet, instead of dispelling the unnatural organ, the Sky Flames harmonized it with the body it was attached to.

While Tsuna was trapped in a trance of some sort, the transplanted arm slowly but surely changed. Skin tone lightening and muscles shrinking, the physical structure of the previously unnatural limb now matched the red-haired boy's other arm.

The Sky Flames however was not done yet; it recognised another faint magical signature that was incredibly similar to its own, yet vastly different at the same time. A great, holy artefact resided in this body, but the lost connection to its true master had weakened it significantly. Such compassionate energy ceasing its existence was unacceptable. The Flames willed itself to supply a trickle of its own power to revive the sacred object, to once more protect and aid its master.

And so, the Sky Flames righted the wrongs, and the balance was restored.

Tsuna broke out of his reverie, and immediately retracted his hand. Confused, he wondered if he had been hallucinating, because the boy's arm no longer looked like that of a Franken-thingy. Well, he would rather see the boy as a human rather than that wretched monster, so he dismissed his earlier suspicion. Then, realising a dying person was still right in front of him, Tsuna clutched the boy's left arm and literally dragged the body towards his house nearby, uncaring of the blood trailing behind them (or, to be honest, trying with all his might not to think about all that red). Maybe Mom had something to patch the boy up with.

And that was the day Sawada Tsunayoshi met Emiya Shirou.

The first thing he could sense was warmth. Then, the scent of grass and morning dew. And for some reason, an image of a cloudless, all-encompassing, peaceful sky flitted into his mind. His other senses were gradually returning, though his mind remained a jumbled mess. But amidst the chaos, a persistent image remained.

Sakura, his brain supplied. Sakura.

All his confusion came to a screeching halt when a soft and wet…something...touched his forehead.

His eyes snapped open. Shirou was moving even before the sound of a startled high-pitched shriek entered his ears, his feet kicking the small, light body in front of him. As his… assailant's (victim's?) body slammed into the wall on the other side of the room, he followed, trapping the smaller figure to prevent escape. His right hand was already clutching a projected Bakuya - a beautiful white Chinese Dao, one of his favourite weapons - as the magus pressed the gleaming blade to his opponent's neck while his left palm pushed the smaller shoulder to the wall.

The next instant Shirou recoiled and quickly dissipated Bakuya into motes of prana as what he was seeing finally registered in his brain.

It was a kid, an adorable one, terrified out of his mind. His doe brown eyes were impossibly wide and his brown gravity-defying hair impossibly fluffy. He was really small, maybe four or five years old, and literally shaking like a leaf.

Good job, asshole. You had scared the shit out of an innocent kid.

Then, the kid shrieked.

"Hhiiiiiiiieee-!"

And promptly fainted.

Disoriented by his sudden wakefulness and the sheer pitch of the sudden shriek, Shirou slowly stood up and examined his surroundings. It was a perplexing sight. The last thing he remembered was sacrificing himself, his body, his mind, his soul, to destroy the Greater Grail, which was located in a vast cave. A young boy's messy bedroom was a universe apart from his life the past week. It made his vision swim.

Was this the boy's room? Did he… did he…what? Find him inside a creepy cave and bring him to his house? The boy didn't look like he could face a chihuahua, let alone go into an unknown cave. Maybe his parents did?

But that didn't even begin to make sense, because any other magi would have killed him on the spot when they had found the Greater Grail destroyed. Or would have brought him home to be dissected so as to examine the Heroic Spirit's arm.

Then a sudden realisation hit him.

Why am I still coherent? He could remember bits and pieces of the past week: saving Sakura by stabbing her with rule Breaker and severing her link to the unborn Avenger, fighting and killing Kirei, holding a projected Excalibur. And pain, so much pain, as well as his resolve to sacrifice himself so that the Greater Grail could be destroyed.

His mind and body should have broken into pieces, unable to handle the corrosive energy and information attacking his body from Archer's arm -

Archer's arm. Which no longer looked and felt like Archer's arm.

Bewildered, Shirou lifted up his left arm, which was supposed to be Archer's transplanted left arm, but saw only his normal, unblemished arm. Normal, as in slightly tanned, but not as dark as the Heroic Spirit's arm, and not as muscular as before. What the hell…?

But as he searched his mind for any of Archer's distinctive memories, he could easily access them without the accompanying crucifying pain which would usually wrack him right after his use of the spiritual arm. That was a pleasant surprise. As he gradually calmed down, he realised that his... vicious assault of the poor boy wasn't really his usual reaction, but that of Archer's. After several millennia of working under Alaya, experiencing all that brutality and devastation, the Counter Guardian had developed an instinctual violent reaction when startled or, in Shirou's case, rudely awakened. Ever since the spiritual arm had been integrated into his body, Archer's habits often bled into his subconscious, unfortunately turning Shirou into a trigger-happy violent person.

Luckily he hadn't Reinforced his legs or the kid would have been a red splatter by now.

His train of thought was interrupted by a muffled "I'm home!" from downstairs. Panicking, Shirou tugged at his hair. Was that the owner of the house? The mother of this child? Was she a magus? But looking at the unconscious boy, the family - if they were indeed a family - was most likely a normal one. He hoped.

But that still didn't solve his dilemma. Kicking a mother's child so hard that he slammed into the wall and then proceeding to hold a blade to his neck until said child fainted from terror hardly made a good impression on anyone's mother.

Including the kid's incoming mother.

"Tsu-kun, I've bought the ingredients for salisbury steak tonight! After Tsu-kun's good deed last night it would be right for us to cele- Oh?"

As the hopefully mother enter the bedroom, Shirou paused in his act of tucking the unconscious boy into his own bed. Silence permeated the air, and Shirou swore the kitchen knife she was holding looked way too vicious for a mundane cooking utensil. He was about to see if the knife contained history worth mentioning when the brown-haired lady turned unexpectedly… bubbly.

"My, you're finally awake, young man! I thought you would be asleep for a few more days, but here you are! That means I should cook an extra portion for dinner! Oh, where are my manners. My name is Sawada Nana and…" Her eyes fell on her unconscious son. "...dear Tsu-kun over there is my son. Oh dear, Tsu-kun must be really exhausted, he has worked so hard to take care of you! He should get the largest portion of steak later, growing boys need more food after all!"

Without even taking a closer look at her son, Nana promptly went downstairs, presumably to cook the aforementioned dinner.

Shirou was speechless. There was no way she could be so naïve that she missed all the warning signs saying 'hey, maybe this young man caused your dear son some pain to the point he unfortunately fell 'asleep'!' What kind of mother left her very young son to deal with a potentially dangerous stranger? (Well, granted not all of his injuries were healed completely and he still felt sore here and there, but he could pose quite the threat!)

And he hadn't even introduced himself!

More Author Notes

Short chap, yeah. I've written 12 chapters so far, and it wouldn't be this short so no worries! The next chapter should update next week, but if people like this and I get a lot of positive reviews, I can update faster.

So, review please! :)