Rei was completely dumbfounded at the sight before him. Somehow, the chakra on his finger turned into a flame the size of a small matchstick 

"Notitia...what is this? Why did my chakra undergo a change in nature...?"

[So you didn't do it on purpose, just as we...I suspected]

"Suspected? You knew this wou-" 

[Lemme stop you right there, we're still not done! Now, continue to increase the power on your finger and don't stop!]

"I...!" 

[No arguing, just do it! Quickly! This is something we definitely need to test!]

Surprised at Notitia's uncharacteristically serious behavior, Rei did as it asked. With haste, Rei focused on the chakra his finger was emitting, increasing it's power more and more until the candle-sized flame became a fire the size of a small house!

"Ngh!!"

[Keep going, don't stop!]

The flames spread through the entire area, rapidly raising the temperature in the area!

"Ahh...this is as easy as it loo-"

BABUMP!

"Uh?!?!?!"

[?]

"Aaahh?!"

[Rei?]

"A-AAAAGGHH!!!!"

[THIS?! REI!]

"AAAARRRRGH!!! IT WON'T!!!"

[STOP USING CHAKRA! STOP USING IT!]

Rei clutched his head as a painful sensation bombarded his chest and brain. Nearly loosing control of fire, he forced himself to stop using chakra in order to put it out

[Rei! Keep it together! Breathe Rei, breathe!]

"A-Agh! My...my chakra going crazy!! Can't control it! Uh?!"

BABUMP!

The flames were gone but, Rei fell on his knees as he clutched his chest in agony. Images began to appear in his mind

{What...what am I seeing right now?! What these images...these...weird...lines}

"Huff...huff...huff..."

[That's it, just breathe. Control the power within you]

Taking a minute, he finally got his body under control

[Good]

"There's nothing good about it?! WHAT THE HELL WAS THAT?!"

[Calm down]

"Don't tell me to-!"

[Unless you want another incident, calm down you idiot]

"..."

[This was unexpected for me too. But at least now, I have a faint idea of what's happening to you]

"Then please explain, how I was able to achieve a change in nature just by focusing chakra on my hand. I know for a fact acquiring elements doesn't work like that!"

[That's...]

"Why did I suddenly undergo a...a panic attack when I increased the output?! Just tell me...just tell me what the hell is happening to me"

[...It's nothing for certain yet but, Raymond...I suspect "Rei" may not be COMPLETELY gone]

"...Huh?"

Shock. That was the only way to describe what he was feeling right now before loads of questions sprouted in his brain. Thinking of the ramifications if such a possibility were true. What did it mean if "Rei" was still alive... and how would that effect Raymond

[Stay calm and listen. The soul...it's the source of everything for everyone in this weird omniversal state we dwell in. In this world, the soul also dictates your chakra, regardless of what body you inhabit. You're a true foreigner to this world which is likely the reason you don't have any natural affinities with it]

Responding with skepticism "No natural...but I've been able to use Inton1Yin/Shadow Styleand Yōton2Yang/Light Style right?!"

[People were initially born with only life/physical energy, Yōton. The Sage of Six Paths gave them spiritual energy in order to connect and understand others. His religion, "Ninshu", was based on this for the goal of peace. EVERY living thing in this world has life, or rather, physical energy/Yōton]

"Okay...but what about Inton? I've shown a talent for Genjutsu have I not?!"

[That's only due to Isshiki's cells within you. He didn't possess the Rinnegan, so he couldn't use all the elements like his partner Kaguya. But he demonstrated the use of Inton with his Genjutsu Tsūshin3Genjutsu Communication technique whenever he contacted his Kara members. You've inherited those powers]

"Spiritual and physical, Yin and Yang, these two energies make chakra. After I 'remade' myself, my power became so much easier to use. Was it so difficult at first because I barely had any spiritual energy at all, because I'm a 'foreigner' to this world?"

[Yes, you barely had any spiritual energy when you first arrived. Now as for why, out of the five elements, you made fire...I believe the original "Rei" had an affinity for Katon. Tapping into his chakra, means your tapping into his soul]

"But 'Rei' should be gone right? And what do you mean by 'tapping' into his chakra?"

[Chakra is the power to connect worlds. The afterlife or "Pure World" is connected to this realm, "The Impure World". That's how people can use chakra to reanimate and/or bring back the dead. But doing so alters the natural balance and thus, is considered forbidden]

"His soul is in the 'Pure world', but I could potentially summon him back to this world? How does that even make sense?! There are plenty of characters in this story who snatch bodies, killing their hosts, and don't have to worry about this"

[Your situation is unique. Your foreign soul doesn't belong here, it's an unknown variable in the "grand scheme" if you will, causing various "imbalances" all over the universe. It's why your actions can effect the course of this story]

"...The 'Ripples'..."

[Causality can be a real bitch. And no one's been able to crack the code yet. Being a respected scientist in your original world, you should know the concept itself is entirely hypothetical, a mere model made by humans. Scientists have sparked longed debates on the subject, some even suggesting it doesn't exist at all]

Rei laid back on the floor, covering his face with his hands as he groaned and lamented

[This entire situation only occurred because of the "Black Scroll's" method. You've stabilized your body and spirit even further, becoming more and more in tune with this world]

"What do I do now? Use a lifeline?"

[I was going to suggest that but...maybe you don't have to waste one]

"This is a serious problem, the kind I wouldn't want to wait around for. If "Rei" returns, I could be forced to leave this body and considering my original body is out of reach, I'll die. I know a soul that doesn't have a body cannot survive in the living world"

[Yeah...but you'd be dying of a technicality on "our" part, and not one of your own making. This is a "fair" game after all]

{Our?}

"What does that mean?"

[I'm gonna talk to the "other" me, the lifeline me for some answers. But it's gonna take a while]

"Should I just wait for you?"

[No, I'll still drop by every now and then, it's just gonna take a while to get some answers. The other me can't stay in this world for too long and you let your first lifeline drag out for a while when you remade your body. It's probably tired...]

{Right, that did go on for quite some time. Even so, I bet I'll still end up with more questions than answers...as usual}

"Last thing, can I not use any elements?"

[No, no, no, nothing so drastic. You saw it earlier, you were able to maintain the flame for quite some time. Even set fire to this whole area before you lost control. Regular Katon shouldn't be an issue, just avoid any high maintenance ones that require a lot of chakra. Rely more on your chakra control for now]

"As for others?"

[Other elements won't be a problem, go nuts. "Rei's" only affinity was fire, the other elements are ripe for the picking. But remember, because you don't have an affinity for them, it's takes much more effort to groom them into useful weapons. Try using clones to cut your learning curve]

"Got it. Thanks for the help Notitia"

[Just doing my job but...thanks? Is someone becoming a Tsundere?]

"I have no idea what that word means, but considering how coy you sounded just now, I assume it's not something I'd enjoy being called"

[Ugh...you're such a non-weeb. I'm gonna head out now. Oh! Before I forget, why don't you start making more of those "Black Rods" in the lab. Weapons that drain chakra will always be handy. See ya!]

"Finally, some useful advice...ugh"

Still a bit winded, Rei got up and left the training area. Heading back to the lab

{Looks like I'm gonna have to be extra careful whenever I use Katon from now on. I should focus on my control the avoid such "issues" from now on}

Making two clones, he sent them on different tasks. One was hard at work manufacturing more weapons, while the other was practicing. Rei himself decided to work on his reserves and visit the Ten-tails again

"I still have my work cut out for me, and I still can't access the rest of the 'Black Scroll'. I need to try even harder!"

♦♦♦

Present time

Suzu, Rei, and Tai had arrived at a training grounds right outside of the village. Waiting for them there was Tango, who in particular had undergone quite the growth spurt himself in the almost two years that have passed

"Barely on time you guys" (Tango)

Tai stepped forward

"Yeah well, Suzu was helping out Mariko and Rei was at the library as usual. Seriously, they should give him a bed considering how often he goes there" (Tai)

"Don't say that, he might actually try to do it" (Tango)

"That's for sure" (Suzu)

"Don't be ridiculous, there's no room for a bed in that cramped library" (Rei)

"..." (Suzu)

"..." (Tango)

"...Wow, you really would live there wouldn't you" (Tai)

Chuckling "Alright enough joking around. It's time for our usual end of the month session. So, who's gonna be the one to pick?" (Tango)

Tai immediately raised his hand

"Dibs. I'm the oldest one anyway" (Tai)

"We're both eleven years old Tai" (Suzu)

"Yeah...but you're a few months behind me, and Rei's only eight" (Tai)

"I'll be nine in a few days" (Rei)

"Whatever...you're still younger, and less handsome than me" (Tai)

Rei rolled his eyes

"You know what, since Rei's birthday is coming up, he should be the one to pick" (Tango)

"Seems fair to me" (Suzu)

"Awww! Dang it...fine!" (Tai)

Tango looked at Rei and questioned him

"So Rei...single? Or group?" (Tango)

"You know me Sensei, single" (Rei)

"Can I take it you'd like to go first?" (Tango)

"Of course, I'm eager to try out some new 'tricks' I've picked up" (Rei)

"Alright then. Tai, Suzu, you know what to do" (Tango)

"Yes Sensei" (Suzu)

"Haaaa...fine! Grouping up would've been faster Rei" (Tai)

"Sue me" (Rei)

Tai and Suzu distanced themselves from Rei and Tango. Tai grumbled to himself

"...Hey Suzu" (Tai)

"Hm?" (Suzu)

"Why's Rei so eager today? Did he hit a wall in his training or something?" (Tai)

"I don't know...he's been on edge recently. Heck, everyone has now that were THIS close to finalizing the peace treaties with Konoha" (Suzu)

"We wouldn't be on edge if our village would ACTUALLY honor the agreement of demilitarization. It's put all the other villages on edge and earned us a shameless reputation" (Tai)

"...I suppose that's true. But you seem to be somewhat nervous as well...why the rush to leave so soon?" (Suzu)

"Haaa...Just have a lot on my plate right now. Need to get back home and sort things out" (Tai)

"Something happen with Ganjō-san?" (Suzu)

"Don't even get me started with Dad. I already heard enough when Kiyoi-ossan-" (Tai)

"You know he gets irritated when you call him 'ossan' right?" (Suzu)

"I know, that's why I do it. But this morning, he gave me news about some, shall we say, 'family drama' going on" (Tai)

"Meaning?" (Suzu)

"Well it's...ugh...you know what, I'll tell you guys later. I'd rather think about something else, let's just watch Rei and Tango-sensei" (Tai)

Folding his arms he leaned back on a tree and said no more. Suzu sat down and didn't pry any further

"Ready Rei?!" (Tango)

"Been ready!" (Rei)

"Heh!" (Tango)

With a wide grin on his face, Tango charged at him!

"SHOW ME WHAT YA GOT!!"