[Kaito will be called Obito from now on. For the betterment of story]
Crack! Black Zetsu was separated from White Zetsu by Kamui and transferred into the dimensional space, and Obito immediately transferred himself into the dimensional space as well.
In the dimensional space, Black Zetsu lay sprawled on a block, its brown pupils glaring at Obito in furious shock.
"Why did you do this! I am Lord Madara's will!"
Obito smiled.
"No, you are not Madara's will. You are Kaguya's will. You falsified the Uchiha Stone Tablet and guided Madara into carrying out the Eye of the Moon Plan, all for the purpose of reviving your mother, Otsutsuki Kaguya!"
Upon hearing this, Black Zetsu was thunderstruck.
"You... how do you know these things? You are absolutely not an ordinary brat. Who exactly are you?!"
"Who I am does not matter. What matters is that you will die here!"
Obito formed the hand seals for Fire Release while simultaneously activating Kamui.
Fire Release: Raging Storm Dance!
Whoosh whoosh whoosh! Amplified several times over by Kamui's warping effect, the roaring flames swept toward Black Zetsu!
Black Zetsu's ability was to sink into the earth and use that power to unleash Wood Release, but inside the Kamui dimension, that ability was completely useless.
"Ahhh!! How could this happen (Damn you)!!"
It was struck dead-on by the flames and let out a scream of anguish.
But it was, after all, the consciousness of that Kaguya, and it was not so easily killed. It shouted at Spiral Zetsu, who was wrapped around Obito's body.
"White Zetsu! Aren't you going to stop this bastard?!"
"..." Spiral Zetsu did not move rashly and seemed to be deliberating.
Obito paused and spoke to Spiral Zetsu.
"Curly-head, now is the time for you to choose sides. Once you make the wrong choice, you had better think carefully about the consequences..."
The standoff held, and after a long silence, Spiral Zetsu's half-amused voice rang out.
"Well, I only care about the urge to defecate. What does the urge to defecate feel like? Obito, if you can tell me..."
Obito smiled.
"Sure. I will not only tell you what the urge to defecate feels like, I will also tell you how feces is formed..."
"It's a deal..." And just like that, lured by the promise of feces, Spiral Zetsu chose a side.
"You bunch of scoundrels!!" Black Zetsu roared in furious exasperation.
"Let's go, Curly-head!"
Crack! Crack! Crack! Wooden branches burst from the Hashirama prosthetic body on Obito's right shoulder, and Obito flung his arm outward violently, sending a shower of branches flying toward Black Zetsu. Black Zetsu scrambled to dodge, but several branches still found their mark.
"This kind of thing..." Black Zetsu gritted its teeth and moved to pull the branches lodged in its body free.
"Don't even think about it!"
Obito raised his hands and formed seals.
Wood Release: Cutting Technique!
Crack crack crack crack crack crack crack crack!!
"Ahhhh!!"
Reverse barbs erupted wildly from the branches, riddling Black Zetsu full of holes!
Obito shifted his hand seals again and, combining it with Kamui, unleashed a Fire Release even more powerful than before!
Whoosh whoosh whoosh!!
"Ahh!! Nearly a thousand years of scheming, and yet I am being destroyed by a green Uchiha brat who has barely stepped onto the stage..."
In a howl of bitter unwillingness, Black Zetsu, the great conspirator who had threaded itself through the entire history of the ninja world, was eliminated by Obito, a newly-arrived transmigrator.
"Hah... hah... hah..."
Obito panted. Because he had Hashirama cells, the chakra in his body was abundant, but he was ultimately someone from another world, and performing hand seals to use jutsu was still not second nature to him, so it consumed more chakra than normal execution would. As he grew more familiar with seals and chakra, that consumption would decrease.
Leaving the Kamui dimension and returning to the cave, the sudden commotion had alerted all of the White Zetsu. They had detached from the Demonic Statue and gathered around in a ring.
Obito stayed on guard and was ready to slip into the Kamui dimension the moment anything went wrong.
At that point, Spiral Zetsu spoke.
"There is no need to worry. White Zetsu share a common consciousness, and besides, we never liked Madara to begin with. He called us inferior artificial humans and used us as chess pieces however he pleased. We artificial humans actually have feelings too..."
"Tobi, you really are a good kid..." Obito sighed, and inwardly breathed a sigh of relief.
Over the stretch of time that followed, Obito did not leave the cave. Under the guidance of the White Zetsu, he practiced the techniques for using chakra, such as gathering chakra at the soles of his feet to adhere to water surfaces and ceilings, as well as other basic techniques, and the use of various fundamental jutsu.
Uchiha Obito's chakra nature affinities were exceptionally comprehensive: Fire, Wind, Lightning, Earth, Water, and Yin. Only the Yang attribute was absent.
Deep in the cave, Obito found the vessels Madara had used to preserve biological matter, and he stored Rin's body in one of them.
In addition, he found a scroll among the ninja tools Madara had prized and kept during his lifetime.
Half a year passed like this, and Obito had reached an entry-level proficiency in every fundamental skill. He was confident that, relying on the power of both eyes' Kamui, he would face not even a shadow-rank opponent without fear.
But... against something at the Six Paths level, his confidence faltered.
Setting aside Otsutsuki Kaguya for the moment.
The enemies who would appear in the future, such as Otsutsuki Momoshiki, Otsutsuki Kinshiki, Otsutsuki Urashiki, and from Boruto's era, Jigen of the Kara Organization, were all immensely troublesome foes.
To stand against them... his current configuration was far from sufficient!
Therefore, the Ten-Tails was essential, and to revive the Ten-Tails, the power of the Rinnegan was needed.
Nagato had a ready pair of Rinnegan, but those eyes' original owner was Madara, and transplanting them would place an enormous burden on him. Only one could be transplanted, and doing so would be equivalent to discarding one eye's Kamui. Obito did not wish to pay such a price.
The Rinnegan evolved from the Sharingan, and it could still make use of the original Mangekyō's powers. Rather than the quick-fix approach of transplantation, Obito would sooner evolve his own eyes himself...
And to evolve the Rinnegan, it was necessary to unite the power of both the Senju and the Uchiha!
Obito currently possessed the dual-eye Mangekyō Sharingan, but... the Senju power was still incomplete. The Hashirama prosthetic body on the left half of his body was nothing more than an ordinary White Zetsu, which was far too inferior!
"The most pressing task is to obtain a complete Hashirama Sage Body!"
Obito raised his head and looked at the Hashirama prosthetic body on the Demonic Statue. According to White Zetsu's description, that prosthetic body had no consciousness, yet it was the highest-fidelity reconstruction and had drawn infinitely close to Hashirama's original form.
However, Obito did not know how to fuse with that Hashirama prosthetic body. Madara had once transplanted chunks of Hashirama's flesh into his wounds and used this to obtain a portion of Hashirama's power, only opening the Rinnegan in his final years. Obito's appetite was far greater. He did not want a portion; he wanted it all!
That meant the method mattered, since Hashirama's power was extremely difficult to wield.
That person should be able to...
The one Obito was thinking of was the individual who held the core technology of the Naruto world and was one of the legendary Sannin: Orochimaru!
"White Zetsu, where is Orochimaru?"
Gurgle gurgle! A White Zetsu burrowed out from the Demonic Statue.
"Orochimaru is in a secret base in the forests of the southern Fire Country, but it seems there are signs he is about to relocate..."
"Then let's hurry and go meet him..."
Whoosh! Obito tore a black cloak from the wall, swung it over his shoulders, and strode out of the base with long, purposeful steps.