Author's Note: I don't know a lot about the Heaven's Feel route, so don't expect me to put in a lot of elements of that.
Disclaimer – I don't own Naruto nor do I own Fate/Stay Night
"-TO! –ARUTO! WAKE UP NARUTO!"
Naruto suddenly shot up from the ground with a gasp.
"Wh-what…happened?" He asked.
He turned his head and came face to face with his life-long partner.
Kurama, realizing that Naruto was fully awake brought its head back and sat on the ground with his hind legs crossed.
Naruto, on the other hand, stood up and looked around in confusion, "I'm… in my mindscape?"
"What do you think? No place is fouler than your mind, so you should have no trouble recognizing it."
Naruto stood there blankly for a few seconds before he took in Kurama's words and yelled in indignation, "Oi! My mind is not foul!"
Kurama nodded his head patronizingly, "Of course it isn't."
Naruto nodded in satisfaction, "Glad you understand."
"Now tell me what happened, Kurama. The last thing I remember is me being pulled into another world and then… darkness. There's nothing after that."
Kurama narrowed his eyes and started explaining, "The first place we ended up in after teleporting was in a giant fire." He sighed, "If I wasn't stuck in you, I could be having so much fun crushing these puny humans right now. I haven't done that in so long!"
Naruto coughed into his hand, "Focus, Kurama."
Kurama sighed again and continued, "Right, right. After landing in that giant fire, I thought that you would start saving as many people as soon as possible. However, when you failed to respond to all the fire and dying people around you, I thought that you had finally lost the last shred of intelligence that you had left in you."
"Oi!"
"Anyway, when I took a closer look, it turns out that your mind had been reverted to that of a seven-year old's. Not only that, but at the time your previous experiences and memories had been stored away, so all you could basically do at the time was walk around and die like an idiot. Lucky for you, I was there to save your scrawny ass."
Naruto let out a confused expression, "Huh? What do you mean?"
Kurama face-palmed, "I mean that since you clearly couldn't control your body, I took control and helped you survive until someone came to save you."
Naruto let his bangs shadow his eyes and asked in a quiet voice, "Wha-what about the rest of the people there?" He raised his head to look at the fox, "Did you save them?"
The two spent a few beats staring at each other in silence before Kurama broke the tense silence,
"There was nothing I could have done. I-
"Don't make excuses Kurama! DON' T GIVE ME BULLSHI-
"CALM DOWN NARUTO! The reason I couldn't save those pathetic meat-bags was because of you! Look at yourself! Your brain wasn't the only thing that reverted back to a child-like state!"
Naruto looked down at himself and finally noticed something odd. Where there should've been a 17-year-old muscular body, there was a small body of a seven-year-old child.
"Wh-WHAT!? WHAT THE HELL IS THIS!?"
Kurama roared with laughter, "HAHAHAHAHAH!" He slapped his leg with a resounding boom, "Oh my god! This is priceless! The vanquisher of Kaguya and savior of the Elemental Nations, reduced to a little child throwing a tantrum!"
"I wasn't throwing a tantrum!" Naruto defended.
"I beg to differ."
Naruto shot the giant fox a nasty glare that didn't quite have the effect he was hoping for due to his child-like body.
"Continuing on, even I don't know where you are right now, all I know is that- hey! Are you even listening, you dumb brat!?"
"Ahhh, I'm screwed," Naruto groaned, "I'm sooo screwed! What do I do? It's gonna take me twice as long to make it to Hokage now. What to do, what to do? Plus, this is kind of creepy. I'm physically seven but mentally seventeen. Sakura's gonna kill me."
"Oi, brat," Kurama tried,
"I mean, she always hits me when I do stupid things, but this is stupidity multiplied by, like, a million."
"Brat," Kurama tried again.
"And I can't even blame Sasuke since he was the one who kept on rambling about how 'it's not saaaafe'. Ahhh, why did things turn out this way? I should've-"
"BRAT! Good, you're finally listening. First of all, you're both mentally and physically seven years old. Your brain has also regressed to that age. Why do you think you had that giant tantrum just now? Although considering the fact that you're… you, I guess the fact that you acting like a child isn't really that out of character."
Naruto would have retorted, but he was too confused to do so, "Huh?"
Kurama sighed once again, "That. That's what I mean. While you were dumb when you were older, you would have still understood that. That's what I mean by mentally seven years old. Once again your brain hasn't been fully developed, meaning, that you're sorely lacking in things like attention span and information retention right now. It would be more accurate to call you a seven-year-old with the experience of a seventeen-year-old."
Naruto scrunched up his face even more, "I still don't get it."
"Basically you're gonna go through stuff like puberty again," Kurama simplified.
Naruto made a face of horrified realization and yelled in dismay, "NOOOOOOOOOOO! WHYYYYYYYYY? I never should've asked that bastard to send me here! WHY, WHY DID I MAKE SUCH A STUPID MISTAKE?"
"Don't worry," Kurama calmed him, "I'm sure that Uchiha bastard and the rest of your puny village are probably trying to find a way to get you back right now. For now, just wake up and explore this new world. You were bored right?"
Naruto face suddenly broke out in an enthusiastic grin, "Right! Let's see just what kinda world the great and amazing Uzumaki Naruto has arrived in," with that Naruto once again closed his eyes and willed himself to consciousness.
Naruto slowly cracked open his eyes and took in the clean white ceiling above him.
'Where...?'
At that exact moment his nose decided to do its job and gave him an answer.
Antiseptics.
Which meant, the hospital.
'How did I-' Naruto started asking himself before his conversation with Kurama came rushing back to him.
…
He put his arm over his eyes and whispered to himself,
"Dammit, we messed up really badly this time,"
A gentle voice interrupted his quiet lament,
"Hello child. My name is doctor Mayers." Naruto uncovered his eyes, sat up, and looked towards where the voice came from. At his left sat a middle-aged, brow-haired woman in a white doctor's coat.
"Are you talking to me?" He asked hesitantly.
Dr. Mayers chuckled, "Who else do you think I was talking to?"
Naruto rubbed the back of his head and let out a sheepish chuckle, "Ahh sorry, my name is Naruto, Uzumaki Naruto. Also, I don't really recognize this place. Where am I and… what happened?"
The doctor sighed sadly and looked at Naruto with slightly moist eyes, "Oh you poor child. To suffer from such a tragedy at such a young age,"
The doctor thought about the incident for a moment and then continued,
"No one actually knows what happened. All we know is that a fire just spontaneously appeared in the dead of the night and before we knew it, the fire had spread far beyond anyone's control. You... you were the only survivor."
Naruto closed his eyes in silent prayer for the dead before he quietly replied,
"I see."
The two spent a few minutes in silence before Dr. Mayers spoke up once again,
"Naruto-kun, we gave you a full-body check-up and made sure to help you recover in any way possible- and let me tell you, you recovered abnormally fast-, but please try moving and tell me whether it hurts anywhere."
Naruto grinned, hopped off his bed, and did a little dance, "Heh! I feel perfectly fine! I-"
Suddenly he froze and thought to himself, 'No, there's something wrong. Something's… missing, but what is it? Everything feels fine…except…for my chakra,' he sat on the ground in a lotus position and tried to force his near-unlimited supply of chakra to the surface, 'No way! I can't use even a little bit no matter how hard I try!'
Dr. Mayers knelt to inspect the blond boy and asked hurriedly, "What's wrong? Does it hurt anywhere?"
The blond let out a nervous smile and assuaged her fears, "It's just-I can feel my chakra but I can't utilize it no matter what."
Dr. Mayers raised a brow, "Your chakra?" She asked.
'You Dumbass!' Kurama's voice rang out in his head like a particularly loud gong. 'Give me control, I'll handle this!' he said.
Naruto tried to let up his control to give Kurama free reign but no matter hard they both tried, it just would not happen!
'What the hell is going on, Kurama!?' Naruto internally panicked.
"Naruto-kun, are you okay? What's going on?" Dr. Mayers asked.
Kurama quickly analyzed the situation and gave him instructions, "Naruto, for now just tell her that nothing's wrong. I'll tell you everything later."
Naruto didn't verbally acknowledge Kurama but when Dr. Mayers once again asked whether or not he was alright, he made sure to follow the tailed beast's instructions,
"I'm fine Dr. Mayers, it's just that- I'm really surprised that I'm not injured at all!"
Dr. Mayers' expression turned even more confused, "And what was that "chakra" thing about?"
Naruto rubbed the back of his head and let out a nervous laugh," Chakra! Right! That was- uhhh – something I saw in my dream! I accidently confused that with the real world!"
The worried doctor let herself relax and let out a sigh of relief, "Heh, I'm glad you're having such nice dreams, but enough of that now, you should get some more rest; your body was actually in a pretty bad condition you know."
Naruto jumped back on top of his bed and gave her a large smile, "Yes ma'am!"
And with that he closed his eyes and once again entered his mindscape.
Inside his mindscape, Naruto lost all traces of the smile he previously had and turned towards Kurama's giant form, "What the hell is happening, Kurama?"
The massive tailed beast frowned, "It seems that this world doesn't know what chakra is."
Naruto let out an indignant snort, "I know that! What I'm asking about is my chakra. What happened? In fact, now that I think about it, even if my body was that of a seven-year-old's, if you could use my chakra then you could've gotten me out of that fire in an instant. So why didn't you? Or could it be that you couldn't use chakra?"
The fox rubbed his chin for a while, then explained, "When I took control of your body, the first thing I tried was using my chakra to get away as fast as possible. The problem though, was that I couldn't. No matter how much I tried, I couldn't use your chakra nor could I use mine. Not only that, but the longer I stayed in control of your body, the more it rejected and fought me,"
He narrowed his ruby eyes,
"I didn't think that the rejection would be permanent. We both still have all our chakra, but for some reason, we just can't use it. That's also the reason we're not dead from the lack of chakra."
Naruto plopped down on the floor and scrunched up his face, "Do you have any other super important things you haven't told me yet?"
"Yes, actually,"
"Really!?"
Kurama touched the surface of the water with the tip of his finger in front of Naruto and the ripples that formed gave way to the form of a shady man with black hair with a black trench coat.
Naruto looked at the picture in confusion, before he turned his head back towards Kurama and raised a brow, hoping for an explanation.
"This is the man who saved you. Hold on, I'll show you the memory."
Kurama once again touched the surface of the water with the tip of his finger and once again, as soon as the ripples cleared, the water reflected a picture. However, this time a burning landscape appeared instead of a shady man.
"Get comfortable and watch."
Suddenly the flames in the picture started crackling erratically, and with a thud, the view jerked violently as if the person holding the camera dropped it or collapsed. Thankfully the place that they fell in was devoid of fire.
There was no doubt though, that in time, the flames would reach that place as well.
For a few minutes, fire roared all around them and all they could see was the orange glow of the flames and the starry sky. The orange glow kept getting brighter and brighter, but before it could reach them, the same shady man in black filled up their field of vision and gasped in surprise and happiness,
"You're alive. You're alive! Thank you! Thank you! I'm so gl-
Before they could keep hearing the shady man continue thanking him again, the scene turned black and then back into clear water.
"At this point your body lost consciousness, and… to be honest I was barely able to keep you alive at that point and if it wasn't for that, you would be…"
Kurama pointed at a blindingly bright golden sheath that were adorned with extravagant engravings and designs.
"what… is that?" Naruto asked.
"At first I thought it was a sheath of some sort, but the more I examined it, the more I realized that in addition to it being a sheath, it's also some kind of powerful item that has a healing ability on par with mine. There might be more functions to it, but on the whole, healing you is the only effect it has had on you."
Naruto tried to digest all that, but it took him several minutes before he finally managed to completely comprehend Kurama's explanation.
Working with a seven-year-old brain sucked.
So this Sheath had saved him from death because it had amazing healing powers, huh. Having something like this would probably make his life much easier, and combine that with Kurama's own healing power…
"Oi Kurama! Does this mean that your healing power and that sheath's healing power can combine and give me some kind of unlimited healing power? That would be sooo awesome! I'm right, right?" Naruto shot up and asked excitedly.
Kurama, however, did not share Naruto's enthusiasm, "Naruto, it's the complete opposite. That sheath has already run out of power and my chakra can barely affect you at the moment. This means that you'll barely have a higher than average healing rate because of my power."
Well that sucked.
Ahhh, whatever!
Even without chakra he was still a badass warrior that could beat anyone! He didn't need any special abilities to do it!
Still, it would have been nice to have some kind of special power to help him out.
"Ah!" Kurama suddenly perked up,
"Because that sheath was inserted in you, you gained some kind of new network for a different power source."
Naruto shot back up, "Really!?"
Kurama nodded before continuing, "However even if you have the network, there's no way for you to use that new power, simply because it's stuck in the same situation as your chakra network."
Naruto sunk back down to the ground, "Damn it Kurama! Stop playing with my emotions!"
This meant that all had to rely on were his mind and physical strength. He had to hone those so that he could…so that he could do what? Was it even necessary to know how to fight in this world? Did this world even allow fighting? Plus, he knew that Sasuke and the others were trying to find a way to get him back, but he wanted to help out too.
Without chakra or any source of power that could allow him to travel dimensions, his desire to help was useless.
Wait!
What if travelling dimensions was commonplace in this world?
Arghhh! Thinking about this stuff would get him nowhere. He needed to first gather some information, and the first step to that was to regain consciousness.
Waking up on the hospital bed was mildly uncomfortable as he was still sleepy and bleary, but he had a goal in mind so he really didn't have time to entertain such thoughts.
Actually… maybe sleeping in just five more minutes wouldn't be such a huge problem.
"Naruto-kun!"
Clearly, Dr. Mayers disagreed.
"You woke up just in time Naruto-kun; the man who saved you is here to see you," she said in a cheerful voice.
Eh? That incredibly shady guy had come to visit him? Why?
Well that guy did look pretty happy that he managed to save a child, so maybe he deserved a chance to improve his image.
The black haired man walked in and his first words were, "I'm here to ask you a question. Would you rather be sent off to an orphanage or would you like to be adopted by a man you just met?"
What the hell? That was way too creepy! He knew that the shady guy would be no good!
Seriousl- huh?
Why… why did this guy seem so… broken?
'Oi, oi, if you look at me like that, there's no way I can refuse you," he thought.
'Always a sucker for sob stories huh?' Kurama remarked.
'shut up,' the blond shot back.
He sighed and finally made his decision, "I'll go with you."
Orphanages sucked anyway.
"Right, I should probably say this now. I'm… a mage."
"What the hell is that?"
'I dunno, sounds tasty though.'