(Author Note: I rewrote the first four chapters a little with the simple intent that Naruto has chakra instead of Ki. This would be all, enjoy.)

Summary: Naruto Uzumaki, the 7th Hokage of Konoha, Jinchūriki of Kurama, hero of the elemental nations, and good friend from many, died from a mysterious illness. Never in his imagination would he have thought to open his eyes inside the body of someone who looked exactly like himself when he was around 18 years old. "Now that's unexpected."

"Speech."

'Think.'

Magic/Technique/Jutsu

Flashback/Events of the Past

Warning: English isn't my native language.

Disclaimer: I don't own any material used in this crossover fanfiction.

'Let's see…' thought Naruto, standing in the middle of a forest. He placed his hand on the ground, and a giant black seal spread from his hand in all directions. When the seal was 300 meters wide, the seal glowed, and a barrier rose and closed the space inside the barrier. Naruto stood up and sighed, having used more chakra than he thought this would take.

'I never realized how much chakra seals really take… at least on this scale. I miss my unlimited chakra reserves. I just got a new sense of respect for Sakura-chan, Sasuke, and others who needed to pay attention to their chakra. Maybe not so when they were adults, but when we were kids, those two needed to calculate how much chakra they could still use… I never needed to think about this,' thought Naruto.

It was Sunday, and that meant he could train the entire day… at least so much he could. He didn't have his unlimited chakra and stamina anymore, and he needed to work on them. This was one of the things he never needed to think about. He would focus on getting a feeling of how well he could really use his chakra. So far, he only used chakra for seals since he couldn't risk getting discovered.

Naruto closed his eyes and felt his chakra flow. He narrowed his eyes before raising his hand, concentrating his chakra into his raised hand. Theoretically, he should have no problems at all controlling his chakra since he could control vast amounts of chakra at once. Controlling the chakra level of a Jonin shouldn't be a problem at all. He should have perfect chakra control with only this much chakra in his body. But this wasn't his body, and even when he had the knowledge inside his brain, his new body didn't have this knowledge.

'My control is good… but not perfect like it could be if this would be my body,' thought Naruto. Blue chakra appeared over his raised hand in the form of a little flicker before it began to grow and spin. A normal Rasengan formed within 2 seconds. Naruto opened his eyes and thought, 'Even when I don't have perfect chakra control, this control is more than enough to perform everything I could do in my past life.'

The Rasengan vanished, and he stretched a little before warming up for his physical training. He would start by training his body before he trained in chakra control and gained back parts of his old skills.

After Naruto warmed up, he would do an intense full-body workout to concentrate on training stamina, overall strength, and speed. He didn't need great physical strength like the Raikage, for example. His Rasengan was strong enough, and he could amplify his punch with chakra to deal more damage. His chakra control was good enough in his new body.

He would also think about ways he could change his usual fighting style to fit his new situation better. The Rasengan would be a central part of it like usual since it didn't cost as much chakra as other Jutsus he used to spam in his past life.

It would be perfect if he could create a new Rasengan that didn't use much chakra but would deal heavy damage to opponents, no matter the size or strength. Normally, he could use Sage Mode and enhance every Ninjutsu of his, but his current chakra reserves weren't large enough to be able to use Sage Mode safely. He would need to get way more chakra. There was a reason why only people like Jiraiya, Naruto, Hashirama, or Kabuto could obtain Sage Mode.

The user needed to have extreme chakra levels to invoke senjutsu, and the body needed to be strong enough to handle and support the enhanced strength. Naruto's body may be back in decent shape for now, but it still needed work to be able to handle senjutsu.

This was another factor why Naruto missed his old body. Even when he was only 16, through his Uzumaki genes and with Kurama inside his body, his body was sturdy enough to handle Sage Mode without a problem.

He chuckled when he thought about everything, 'Even when I hated it at the beginning of my life, being born as a Uzumaki with Kurama inside me was truly a blessing in more than one way.'

Naruto went down and began his intense full-body workout routine with push-ups. Since he created the barrier around him, no one could distract him. He was completely isolated inside this barrier.

After 3 hours of training, he gasped and took a deep breath. 'I have more stamina than I thought,' thought Naruto. Maybe it was also because of his strong willpower. No one ever broke his willpower. It was like an unbreakable diamond. The body could work past its limits if the head commanded it. Willpower was an important aspect of training to break one's limits.

Naruto sat down on the grass and summoned a bottle of water from a storage seal he had placed on his body. He had many invisible seals all over his body, a few of them being storage seals. He took a large gulp, almost emptying the bottle.

"HAH! This is the best!" said Naruto after he took the bottle from his lips. He lay down and closed his eyes for a moment, enjoying the warm sun on his sweaty body. He already took off his shirt in the middle of his workout since it was completely wet from Naruto's sweat. The gentle breeze that blew over Naruto felt amazing.

After he rested for 10 minutes, he slowly stood up and cracked his neck. Three hours of intense, complete, full-body workout was enough for the first day. Now, he would use the rest of the day to get used to his chakra. Being able to create a Rasengan with one hand was just a test of how good this body was at chakra control. But this was only a general categorization.

'Alright… let's do this,' thought Naruto.

The barrier broke, and Naruto walked away, exhausted but satisfied with his results and gained knowledge. He needed 4 hours, but he got a full overview of how his new body worked when it came to chakra. His chakra control was better than he first thought. Since this body never worked on elemental manipulation… since this concept of chakra usage didn't exist yet in this world, he would need to train from the ground up. Having the knowledge about the theory didn't give his body the ability to use it instantly. He would also need to start on his Kenjutsu training with Silent Shadow; once he got a few basic skills done where, he could say he mastered them to perfection again, like the Shunshin no Jutsu (Body Flicker Technique), his beloved Rasengan (Spiralling Sphere), the Kawarimi no Jutsu (Substitution Jutsu), elemental manipulation, and his taijutsu skills.

Different from when he was little, he would train one skill to perfection before he would train another. He smiled when he thought about all the things he would need to learn again from the ground up. It was maybe silly, but having to train so hard again brought back good memories from all the times he trained for those techniques back in the elemental nations with his old masters.

He would cherish those memories and enjoy the challenge he would have once again. Only this time, he couldn't use his Kage Bunshin (Shadow Clones) to help him train. He could most likely make only a few before his chakra was used up. Sadly, he could never use this method again, at least in this world. His reserves just weren't large enough, and they would never be. It was more effective to train without them to spare chakra.

"Did you perhaps remember something, Naruto? Your training showed me that you know exactly how someone should train his body. There would also be the fact that you did many exercises to figure out how your chakra feels and how it works in your body. It was like you tried to figure out how your body feels."

'Believe me or not… but everything I did was more like intuition than anything else. After I had read about chakra in the book of the Assassin King, I felt that I knew something. When I trained, I followed some guidance from the information in the book and my intuition. But you are correct when it comes to getting used to my body. I was an Assassin before I fell into a coma and lost all my skills,' thought Naruto.

Naruto would go along with his lie for now… even when he still didn't like it. It would be best if no one ever found out that he wasn't the Naruto Uzumaki from this world. Otherwise, he could get the attention of powerful enemies, especially after he had received information about all the powerful beings in this world from his new partner.

"I will believe you for now since it doesn't matter to me anyway. My only desire is to assist you in your future fights and to be used in a fight," said Silent Shadow in Naruto's mind.

Naruto chuckled and thought, 'Sorry, partner, but you will have to wait a little bit. I need to learn how to wield you properly first, but before I do this, I need to learn some basic survival skills that were mentioned in the book again.'

After 20 minutes of walking, he entered Kuoh again. He stretched again and sighed in satisfaction when his lower back cracked. The tightness that was built up during his training was released during the crack. It was always a liberating feeling when the tightness in the bones or muscles vanished.

Naruto had both eyes closed and let his senses guide him through town. One other thing he needed to build up again was his five senses. They weren't what they could be. Having sharper senses was always a good thing. This way, he could react to all kinds of situations faster.

He opened his eyes when he came to a street. He needed to wait since a few cars were passing by. The sun was slowly lowering itself over the horizon and thus bathed the entire city in an orange light.

He didn't say anything when a woman walked up to him and waited beside him. Naruto and the woman crossed the street when no more cars came. Both were walking next to each other, remaining silent.

Naruto didn't look at her, knowing that this woman was the first one who visited after he woke up. Now that he knew what the energy from her was, he knew that this woman was a fallen angel. After he got all the information from Silent Shadow about the other races, he slowly but surely got a feeling for what energy belonged to what race. The energy he felt right now was holy energy, but not as pure as it could be. The holy energy of a fallen angel was slightly corrupted since they lost god's blessing and fell from grace. It was still very effective against creatures of darkness like devils, vampires, or yōkai.

"I wondered when you would show up," said Naruto when both stopped at a bench in a park. Naruto and the woman walked together to the park in Kuoh, which wasn't far away. Naruto would have to walk through the park to get to his apartment anyway, so it wasn't really a large extra mile for him to walk.

"You really changed, Naruto," said the woman.

Naruto sat down on the bench and chuckled. "What can I say? I lost all my memories when I woke up. I didn't even know my name when I woke up, and I don't remember anything so far. The possibility that I am different than before is high," said Naruto.

The woman sat down beside Naruto and looked at Naruto's satisfied, carefree face. It was truly new to her. The old Naruto always had a scowl on his face or a stoic expression. He had a cold personality and almost no friends because of his loner attitude. Even when he cared deeply for his comrades, he didn't show it very well. Almost everyone had something against the old Naruto.

The Naruto the woman saw now was the complete opposite. The way he spoke, he looked, and the feeling around him changed completely. It was hard to see this completely different side to the Naruto she had known for almost three years now. But nonetheless, she couldn't help but smile a little… something she didn't do in a while.