With Karin's physical data from her Rinnegan awakening phases readily available, Shinji could easily pinpoint the issue.
As he flipped through the records, the confusion in his eyes deepened.
Logically, with his mastery of a pair of Rinnegan and a pair of Koryugan, his dojutsu power far surpassed Karin's. Thus, when fusing with the First Hokage's cells implanted in his body, the resulting 'All Creation Power' should have been greater than Karin's post-surgery output.
"Where did things go wrong?"
Forcing himself to calm down, Shinji began to analyze.
Awakening the Rinnegan was his key to countering the Hegemon. Without his own Rinnegan, relying solely on his Eternal Mangekyo Sharingan to wield Karin's Rinnegan through 'Susanoo Tomoshibi' would barely qualify him to become the Ten-Tails Jinchuriki.
This step could not fail!
Back in his study, he pored over notes, reviewing every detail.
"Before the surgery, my condition was normal. The first two days post-surgery showed minimal deviation. The real issue started on the third day."
Shinji furrowed his brow, recalling his actions over the past few days.
After careful reflection, he found no anomalies. Knowing this was a critical period for awakening the Rinnegan, he had lived quietly, avoiding extreme actions or bodily experiments.
"So where's the difference between me and Karin post-surgery? This is strange!"
Shinji propped his chin, his face full of doubt.
Suddenly, a flash of insight struck.
"Could it be…?"
Shinji narrowed his eyes.
If there was a difference, there was one glaring distinction between him and Karin post-surgery, something he had overlooked because he was so accustomed to it.
That difference was none other than his dojutsu, 'Susanoo Tomoshibi.'
Or more precisely, his use of 'Susanoo Tomoshibi' to wield the Rinnegan and Koryugan.
Karin, post-surgery, hadn't been wielding any other eyes!
Rising quickly, Shinji headed to the underground training area. Without hesitation, he activated 'Susanoo,' then used 'Susanoo Tomoshibi' to release the Rinnegan in the second pair of eye sockets and the Koryugan in the third, carefully removing them.
After placing the Rinnegan and Koryugan into small nutrient containers, Shinji closed his eyes to sense the change.
Since awakening his Mangekyo Sharingan and mastering 'Susanoo Tomoshibi,' he had always wielded various eyes—Mangekyo Sharingan, Byakugan, Hogan, Ketsuryugan, and the more powerful Rinnegan and Koryugan dojutsu Bloodline Limits.
This state of wielding no eyes at all felt utterly foreign to him.
"Feels a bit strange!"
Shinji opened his eyes and chuckled.
Without the Rinnegan and Koryugan, he could clearly feel his dojutsu power plummet, losing access to their various techniques.
But as he suspected, though he lost much dojutsu power and techniques, he felt significantly lighter—physically and mentally—as if he had shed a heavy burden or removed a cumbersome weight.
"When I used 'Susanoo Tomoshibi' to wield the Rinnegan and Koryugan, I gained immense dojutsu power and powerful techniques, but I unknowingly took on a heavy burden. Perhaps this burden prevented my Yin Release chakra from freely fusing with the Yang Release chakra in the First Hokage's cells."
Shinji felt he had uncovered the truth.
His dojutsu 'Susanoo Tomoshibi' essentially enslaved the wielded eyes.
His Yin Release chakra had to constantly suppress these eyes to prevent them from overpowering him.
In his current state, he was wielding stronger powers with weaker ones.
He was using his Eternal Mangekyo Sharingan to control a far superior Rinnegan and a Koryugan on par with his own eyes—a delicate balancing act.
Fortunately, the suppression of 'Susanoo Tomoshibi' made rebellion unlikely. Otherwise, a single Eternal Mangekyo Sharingan could never stably control a Rinnegan and Koryugan.
"Hm?!"
As Shinji pieced this together, he felt his body's chakra reactions surge.
The Yin Release chakra, previously consumed in suppressing the Rinnegan and Koryugan, became lively, wildly fusing with the Yang Release chakra in the First Hokage's cells.
A surge of 'All Creation Power' formed within him, nourishing his body and his Eternal Mangekyo Sharingan.
Freed of its burden, his Eternal Mangekyo Sharingan's dojutsu power skyrocketed!
"Just as I thought!"
Shinji was elated.
Without instruments, he could feel his chakra strength growing at a rate matching Karin's normal post-surgery levels—or even surpassing it!
After savoring the sensation, Shinji tempered his joy and looked at the two nutrient containers holding the Rinnegan and Koryugan.
For now, during this critical phase of awakening the Rinnegan, wielding any dojutsu Bloodline Limits was unsuitable.
"Should I return the Rinnegan to Karin and the Koryugan to Yakumo?"
The thought crossed his mind.
He knew that storing eyes in nutrient containers, no matter how often the nutrient fluid was changed, would slowly deplete their dojutsu power.
Conversely, nurturing them in suitable hosts would enhance their power.
For instance, during the time he entrusted the Koryugan to Yakumo, its dojutsu power rose from slightly above a Mangekyo Sharingan to rivaling his Eternal Mangekyo Sharingan.
Returning the Rinnegan to Karin and the Koryugan to Yakumo would not only boost their strength but also nurture the eyes' dojutsu power through their chakra.
After weighing the options, Shinji picked up the containers, shaking his head. "Forget it. I'll keep them for now."
Considering he might still need these eyes, he decided to hold onto them temporarily. Swapping eyes back and forth was troublesome, and once he awakened his Rinnegan, he planned to use these eyes for experiments he had long considered.