The key to everything was first restoring that damaged pair of Mangekyō Sharingan. As for why he didn't fuse Uchiha Fugaku's Mangekyō with the pair of Mangekyō in Karin's eye sockets, Uchiha Shinji had his reasons.
Uchiha Fugaku's Mangekyō was a backup for him.
If Sasuke couldn't obtain Itachi's Mangekyō in the future, then Fugaku's pair could serve as insurance, ensuring Sasuke could still awaken the Eternal Mangekyō Sharingan that contained the chakra of Ōtsutsuki Indra.
Thus, unless it was absolutely necessary, Shinji wouldn't easily use Uchiha Fugaku's Mangekyō.
"No rush, I'm still young. I can take my time and plan."
Shinji calmed himself down.
The power of All-Creation Power was a high-level force in the shinobi world, representing the threshold to the 'Six Paths' level. Throughout millennia, very few people in the shinobi world had ever mastered such power.
Therefore, these things couldn't be rushed. They required the right timing, circumstances, and people.
For now, Shinji's starting point was already very high, and with the path trodden by Uchiha Madara ahead as a reference, he had a clear route to follow.
Moreover, the current reincarnations of Ōtsutsuki Indra and Ōtsutsuki Ashura were right beside him.
As long as he boldly hypothesized and carefully tested, slowly feeling his way towards the power of All-Creation Power and advancing toward the Rinnegan wouldn't be an unattainable goal.
Closing his eyes, Shinji emptied his mind of all distractions and began organizing his plans.
First, he would regularly exchange chakra with Karin to enter a shallow 'Yin-Yang fusion' state. This would not only enhance both their chakra qualities but also allow them to gradually explore techniques for fusing Yin and Yang chakra properties.
Second, he needed to find a way to restore that fully damaged Mangekyō and fuse a second pair of Eternal Mangekyō Sharingan.
These two tasks would be his primary focus in the near term.
After deactivating Jikibi and Wazunagi and closing his Eternal Mangekyō Sharingan, Shinji exited the small forest and began heading back to his apartment.
On the way, he recalled how the Hidden Leaf had convened the other shinobi villages to discuss dealing with the Akatsuki.
"How strange… What's going on inside the Akatsuki?"
Logically speaking, the Akatsuki should have been fully assembled by now and wouldn't need to recruit more members. But with the recent escape of Moryo, there were clear signs of the Akatsuki's involvement, and Obito had even personally stepped in to rescue Moryo. This was unusual.
Unable to come to any conclusion, Shinji thought to himself, "It looks like I'll have to find an opportunity to use Jikibi to contact Deidara."
Clearly, Shinji had overestimated the internal unity of the Akatsuki, so he hadn't initially considered the possibility of internal conflict.
In truth, both Nagato and Obito were deeply wary of each other.
Obito, of course, could never fully trust Nagato and Konan, given his involvement in Yahiko's death and the destruction of the original Akatsuki members. And having discovered some clues, Nagato and Konan continued to work with Obito while remaining cautious of him.
Konan had even prepared six hundred billion explosive tags, enough to sustain ten minutes of continuous explosions, just to ensure Obito's death.
But since their goals aligned, in the original timeline, they maintained a fragile alliance until they had collected all nine Tailed Beasts.
This was why Shinji hadn't considered the possibility of infighting within the Akatsuki.
However, what he didn't realize was that his actions had unintentionally disrupted this fragile alliance.
His impersonation of an Akatsuki member made both Nagato and Obito suspicious that the other was secretly gathering strength.
Neither side was willing to trust the other enough to communicate openly.
Having missed the opportunity for an honest conversation, Nagato and Obito were left with no choice but to secretly recruit allies, preparing for the inevitable future conflict.
Thus, Obito recruited Moryo and Shennong, while Nagato sent Sasori to recruit Hiruko.
The chain of events leading to this tension had all been set off by none other than Shinji himself, the very person now fretting over the consequences.
"I wonder how the village plans to deal with the Akatsuki…"
Shinji shook his head.
Then, he remembered how the Hidden Leaf had convened the other villages to discuss dealing with the Akatsuki, something Neji had mentioned, and recalled Neji's sigh at the time.
On a sudden impulse, Shinji disappeared into the night with a flicker of movement.
In a training field not far from the Hyuga compound.
Clang! Clang! Clang!
Neji deftly dodged and blocked as countless kunai were launched at him.
His movements were agile, each step a graceful maneuver as he deflected kunai with the one in his hand, causing sparks to fly in the darkness.
"So strong!"
Lee stood on the sidelines, eyes wide with amazement.
Tenten, who was operating the mechanism that fired the kunai, said, "Of course! He's Neji!"
Lee clenched his fist. "I must catch up to him!"
"You'll have to work hard for that!"
Tenten smiled and then turned her gaze back to Neji, her eyes full of admiration for his strength.
Whoosh!
Just then, it seemed Neji was growing tired, as he failed to fully dodge a kunai. It grazed his cheek, leaving a shallow cut.
"Careful!"
Tenten exclaimed and immediately stopped the mechanism.
In the center of the field, Neji called out, "Why did you stop?"
Tenten replied, "Neji, your face…"
Neji wiped the blood off his face. "It's nothing. Continue!"
Seeing Neji's heavy breathing and his trembling hands barely gripping the kunai, Lee said, "Neji, let's rest for a bit."
Tenten agreed, "Yeah, training in this state is dangerous. Let's take a break."
Neji glanced at them. "Do you think I can't handle it?"
Both Lee and Tenten shook their heads in unison.
"Let's continue, I'm fine!"
Neji got into position, urging them to resume.
Seeing his determination, Tenten sighed and restarted the mechanism.
In an instant, a barrage of kunai flew at Neji once more.
Lee, clenching his teeth, thought, "If even a genius like Neji works this hard, I can't afford to slack off! Starting tomorrow, I'll double my training!"
Tenten sighed at Lee's remark, shaking her head in exasperation.
But as she looked back at Neji, her eyes showed a hint of concern.
She understood that Neji was pushing himself to compete with Sasuke.
What she couldn't understand was why Neji, already so exceptional, felt the need to compare himself to others and push himself this hard.
Just as she feared, Neji, exhausted, was having close calls in the training field, and Tenten's hands were starting to sweat from the anxiety.
After a while, Tenten couldn't bear it anymore. "We have to stop!"
Lee agreed, "It's time to stop!"
Tenten reached to shut down the mechanism.
"No!"
Neji, panting heavily, shouted.
Tenten's hand froze mid-air, unsure of whether to proceed or retreat.
Suddenly, something unexpected happened in the field!
Neji stumbled, his footing faltering. His rhythm was completely broken, and the defense circle formed by his Byakugan, Gentle Fist, and kunai collapsed instantly.
Now defenseless, Neji was exposed to the barrage of kunai from all directions!
Tenten gasped in horror and reached to stop the mechanism.
Lee, gripping his kunai, charged into the field.
But both of them, standing on the sidelines, were too far away to intervene in time.
"Revolving Heaven!"
In a moment of life and death, Neji let out a furious roar from his chest!
As he stumbled, he began spinning, his entire body becoming a whirlwind, meeting the incoming kunai head-on!
Clang! Clang! Clang!
In an instant, the sound of metal clashing filled the air. The kunai, striking the vortex Neji had created, fell to the ground as though they had hit an impenetrable wall!
"This…!?"
Both Tenten and Lee were dumbfounded.
They hadn't expected Neji to turn the situation around so easily in such a dire moment. They were frozen in place, Tenten even forgetting to stop the mechanism.
However, maintaining a technique like Rotation in his exhausted state was beyond Neji's capability.
After only a few breaths, Neji was forced to halt his technique, once again leaving him vulnerable to the incoming kunai.
"No!"
Tenten screamed, realizing that she couldn't stop the mechanism in time.
In the center of the field.
"So this is how it ends…"
As Neji watched the kunai hurtling toward him, his body aching and drained of strength, a strange sense of relief washed over him.
But in the next moment, he was filled with regret.
Thinking of his wrongly accused father, and the cursed Caged Bird Seal on his forehead, he was consumed with frustration. But no amount of regret could stop the storm of kunai coming his way.
And in that moment!
A flash of golden light appeared, and a massive golden skeletal hand grabbed Neji.
The kunai from all directions clinked harmlessly off the golden skeletal hand, falling to the ground in a series of soft thuds.
"What is this…"
The resigned Neji was momentarily dazed.
He immediately recognized the golden skeletal hand as Susanoo, the Mangekyō Sharingan technique used by that mysterious Uchiha when they fought Moryo.
But Susanoo wasn't supposed to be here, so he thought, "Am I already dead? Is this an illusion before I die?"
It didn't take him long to realize that he wasn't dead. The golden Susanoo was really there!
Steadying himself, he turned and saw the cloaked figure in the Akatsuki's red cloud robe, wearing a mask.
As the figure deactivated Susanoo, he said, "Were you really in such a hurry to die?"
Neji, stunned, asked, "Why… why are you here?"
The immense power of this man instinctively made Neji use honorifics.
The figure chuckled. "Why shouldn't I be here?"
Neji quickly glanced toward the sidelines.
He saw that Tenten and Lee had somehow been caught in a genjutsu, lying unconscious on the ground. The mechanisms around the field had also been precisely hit by a kunai, stopping them from firing.
The figure looked around and remarked, "The move you just used, that was the Hyuga clan's Revolving Heaven, wasn't it?"
"Yes!" Neji nodded.
"Just learned it?"
Neji didn't hide the truth. "Yes, I hadn't mastered it before, but I managed to use it just now for the first time."
"Extreme situations really do unlock potential." The figure smiled. "But if I hadn't passed by, the Hyuga clan would be preparing a funeral."
Neji lowered his head and quietly said, "Thank you for saving me."
"Luck won't always be on your side."
With that, the figure turned to leave.
Neji hesitated before calling out, "Please wait!"
The figure stopped.
Neji asked, "Why… why did you save me?"
The figure paused for a moment, then smiled. "Perhaps I thought it would be a waste."
"A waste?" Neji asked incredulously. "Why would it be a waste for someone as mediocre as me to die?"
The figure turned back to face him. "Because I don't think you're mediocre."
Neji was stunned.
He couldn't believe that this powerful figure who could crush demons considered him anything but mediocre.
After a brief moment of surprise, he said bitterly, "But I can't see any future for myself. My Byakugan is far inferior to your Mangekyō Sharingan."
The figure responded matter-of-factly, "Of course, the Byakugan is inferior to the Mangekyō Sharingan."
Neji's face fell.
The figure continued casually, "If you want to compete with a Mangekyō, you'll have to unlock the Tenseigan first."
Neji perked up. "T-Tenseigan! What is that!?"
He had never heard of such a thing.
But for some reason, when it came from this mysterious figure, he was certain that the Tenseigan must be real.
The figure replied calmly, "The Tenseigan is the next stage of the Byakugan."
Neji's whole body trembled with excitement. "The Byakugan can awaken into a higher-level dojutsu, like the Sharingan!?"
The figure nodded.
Neji, deep in thought, asked, "But why have I never heard of this? Why isn't there any record of it in my clan?"
The figure looked up at the night sky. "Can you see it?"
Neji followed his gaze but saw nothing unusual in the night sky except for the moon and stars. "I don't see anything."
The figure said, "That bright moon up there—how can you not see it?"
Neji blinked. "The moon?"
The figure spoke solemnly, "The secret of the Tenseigan is hidden in the moon above us. Only by finding a way to reach the moon can you unlock the Tenseigan."
Neji, now even more confused, asked, "A way to reach the moon?"
The figure nodded. "That's why I'm here."
Neji glanced toward the distant Hyuga clan compound and understood: "You mean… the way to the moon is hidden within the Hyuga clan?"