What kind of power would Kotoamatsukami gain once its Mangekyō Sharingan evolved into a Rinnegan?The original storyline gave no useful hints.
Mainly because Kotoamatsukami was already absurdly overpowered, much like Kamui. And it never truly came together as a full pair of eyes.
Not until Aoba arrived and cultivated Sasuke into a true Six Paths–level Uchiha did this officially strongest genjutsu eye finally evolve into its Rinnegan state.
Once upgraded, Kotoamatsukami's Rinnegan had only one terrifying ability: Tenmyō Reikō (Heavenly Radiance of the Soul).
It transformed the technique from a purely mental genjutsu into a full-blown soul-based attack. Upon activation, it would drag the target's soul into a space filled with mysterious divine light, what was known as Reikō.
This Reikō had two primary effects:
Shatter and Reconstruct.
Both applied directly to the target's soul.
Once caught, the caster could completely shatter the soul inside that light. Or, if they didn't wish to kill the target, they could go one step further, reconstruct it.
A shattered soul became a blank slate, and in the reconstruction process, the caster could freely reshape the target into any kind of person they desired.
Whether it was muscle memory, emotional memory, or soul memory, none of it remained. This was a method to reshape a person from the very root.
Shattering alone was manageable, but soul reconstruction was extremely taxing, and could only be used on one person at a time. Still, once the target was caught, not even Sasuke's Tendō Ōmiya or Kakashi's Infinite Domain could resist this soul-level technique.
This was a top-tier ability meant for elite battles only, much like the original Kotoamatsukami, it was basically useless against cannon fodder.
Once Toneri's soul was reconstructed, he had become a completely new Konoha shinobi. Following Aoba's instructions, Itachi gave Toneri a detailed new life plan, reshaping him into a totally different person.
But none of this affected Toneri's combat strength.
After completing his Ōtsutsuki genetic enhancement, Toneri now possessed the true body of an Ōtsutsuki.
The chakra within him even exceeded that of Hashirama's natural Sage Body. He was born with all six chakra natures. The only thing missing was a pair of Sharingan or Rinnegan, and he'd become a full Seven-Nature Chakra wielder, reaching true Six Paths–tier power.
The only "regret" was that Toneri hadn't immediately awakened the Rinnegan. But that was expected. Even among the Ōtsutsuki clan in canon, few were shown with Tenseigan, let alone Rinnegan.
Most Ōtsutsuki preferred using chakra fruits or pills to forcibly awaken Rinnegan and boost their power.
"How do you feel?"Aoba asked Toneri.
"Hard to describe... I can sense that my Byakugan is reaching its peak, but something's still missing."
"What do you mean?" Toneri's words sounded contradictory.
"Hmm... it's like... this body of mine... is too young."
"..." That was a bit abstract—but Konoha's top scientists were overseeing this project. Soon, someone understood what he meant.
"Is it that your eyes and body aren't syncing?"
"Not exactly. Actually, I feel great, there is no mismatch at all. My body is young, powerful, and full of vitality. But because it's too young, there's a minor issue. Even if I don't do anything, the problem will resolve itself soon."
"Understood. It's likely a self-protection mechanism between your body and your eyes. It's similar to how Sasuke's Sharingan awakened unusually late, his body was protecting itself. Awakening too early would've placed too much burden on him. Your body is probably acting the same way. Normally, the Tenseigan would awaken around adolescence. Even if your body has already reached the conditions for activation, its instincts haven't caught up yet."
"That's exactly it. I just need to move around, fight a bit, and let my body adjust. Then I should be able to awaken the Tenseigan quickly."
"Perfect. Start the procedures for Neji and Hinata as well."
With everything arranged, Aoba headed to Madara's private training grounds.
Not long ago, he had sensed Madara's chakra growing increasingly powerful.Madara had received the custom-bred Mangekyō pair: Parting and Elysium. He preferred direct offense/defense eyes like these.
And he had refused Sasuke's help in awakening the Rinnegan, insisting on doing it himself, using Konoha's resources and research.
If anyone else had said that, Aoba would've refused outright.But this was Madara, a man who had already done it once on his own.
For his second attempt, Madara had a younger body, far greater chakra reserves, his own prior experience, and the full support of Konoha's research division.
This time, his awakening process went incredibly smoothly.
On the 7th day of training, Aoba sensed that the Mangekyō had reached its limit.
By the 10th day, signs of breakthrough had appeared.
On the 12th day, a completely new chakra signature burst into existence.
Madara had succeeded.
It was far more strenuous than Sasuke's awakening, because Sasuke had reached Six Paths level first and then reverse-engineered his Rinnegan. With Aoba's chakra inheritance, Sasuke had overwhelming chakra reserves, far beyond Madara.
While Madara's new Rinnegan lacked Sasuke's sheer visual power, it didn't matter to him, because this eye was awakened by himself. His mastery over it far exceeded that of Kakashi or Itachi.
"Lord Madara, congratulations on achieving the Rinnegan once more."
"Hmph. Don't think I don't know... this is already Konoha's fourth Rinnegan pair, isn't it?The so-called 'eyes of the Sage', you're producing them in batches now. You really are something else, boy."
"Heh, only four pairs. That's not much. You still have spare Sharingan, don't you, Madara-sama? Give me a bit more time, and I can manufacture even more Rinnegan."
Madara was speechless.
As an Uchiha, he had once revered the Rinnegan. Back then, awakening it by his own hands filled him with pride and arrogance, even if he never showed it.
But now, revived and reborn, he had once thought his Rinnegan would make him unrivaled in the shinobi world.
And here they were, just a few years later, Rinnegan were practically being mass-produced.
He couldn't help but feel a strong sense of unreality.
Four pairs of Rinnegan, and more on the way. Madara was beginning to understand Aoba's true strategy.
If you would like to read more...
The novel has be completed (Chp. 362) on the patreon -> SaintXI