Three days passed in the blink of an eye.
During these three days, the dojutsu power of the Rinnegan in Karin's eye sockets gradually slowed its growth, stabilizing.
Thus, Shinji used 'Jikibi' to notify Karin in advance and, as planned, arrived at her apartment that evening to extract the Rinnegan.
At night.
After welcoming Shinji into her apartment, Karin asked nervously, "Leader, are we performing the eye extraction surgery tonight?"
"Mm!"
Shinji nodded lightly.
Karin felt a bit reluctant. After all, this pair of Rinnegan had evolved step by step from restoring a fully damaged pair of Mangekyo Sharingan. To say she had no attachment to them would be a lie.
Noticing Karin's sentiments, Shinji said, "This pair of Rinnegan is crucial to me right now. But rest assured, once I've accomplished certain things in the future, I might return them to you."
Karin quickly explained, "Leader, I'm just a bit reluctant, not greedy…"
"I know!" Shinji interrupted her explanation. "If you hadn't poured your heart into them, they wouldn't have awakened for you. You are their true owner, and no one can change that!"
Seeing that her leader understood her, Karin let out a soft sigh of relief, then obediently lay on the bed, awaiting the eye extraction surgery.
Shinji wasted no time and began preparing for the procedure.
For him now, an eye transplant was a minor surgery that took only a few minutes. He took out the surgical tools and a nutrient canister containing Karin's original eyes, then started the operation.
A few minutes later, Shinji successfully removed the Rinnegan from Karin's eye sockets and replaced them with her original eyes.
Staring at the Rinnegan floating in the small nutrient canister, he confirmed that its patterns hadn't degraded, then carefully tucked it into the shinobi pouch at his waist.
Karin, now with her original eyes, sat up from the bed.
She looked around in a daze, finding everything blurry and indistinct.
At that moment, Shinji handed her a pair of glasses.
After putting them on, Karin's vision cleared slightly. Staring at her hands, she murmured, "So this is what my own eyes are like… I'd almost forgotten."
Karin's original eyes were slightly nearsighted, requiring glasses to see clearly.
The eyes Shinji had transplanted into her, even the weakest of them, were Mangekyo Sharingan, followed by Eternal Mangekyo Sharingan and then Rinnegan. Switching back to her own eyes felt incredibly unfamiliar.
Though she had lost the Rinnegan, her enhanced physique and immense chakra remained. She could still use the Uzumaki clan's sealing techniques and 'Wood Release,' so if she went all out, her strength would still be among the top of her peers.
Shinji said, "It might take some time to adjust."
Karin smiled, "Have you forgotten how I restored that fully damaged pair of Mangekyo Sharingan? Back then, I couldn't see anything at all!"
"Mm!" Nodding, Shinji instructed, "From now on, stay on standby. We may soon counter-invade the Demon world, so be prepared!"
"Yes!"
Karin's smile faded, and she nodded solemnly.
Without further words, Shinji turned and left Karin's apartment.
He then stealthily slipped out of the village, heading straight to his secret laboratory outside.
In the spacious testing area, he activated his Eternal Mangekyo Sharingan, summoning 'Susanoo,' while retrieving the small nutrient canister with the Rinnegan from his shinobi pouch.
"Rinnegan…"
Taking a deep breath, he activated 'Susanoo Tomoshibi,' removing the 'Koryugan' from the third eye socket of his 'Susanoo.' Then, using 'Susanoo Tomoshibi' again, he placed the Rinnegan from the nutrient canister into the third eye socket.
Roar!
The moment the harnessing was complete, his 'Susanoo' let out a furious roar!
Shinji clutched his eyes.
A sharp pain spread through his optic nerves, a sensation he had never experienced despite harnessing so many eyes.
It took a long while for the pain to subside.
"Phew…" Shinji exhaled deeply, then remarked, "Harnessing the strong with the weak is, as expected, no easy feat!"
When Karin's Rinnegan was still an Eternal Mangekyo Sharingan, its dojutsu power had already surpassed Shinji's own Eternal Mangekyo Sharingan.
Now, having evolved into the Rinnegan, its dojutsu power had increased dramatically, widening the gap even further.
Thus, using his significantly weaker Eternal Mangekyo Sharingan to harness this pair of Rinnegan was, understandably, quite difficult.
Fortunately, the 'Susanoo Tomoshibi' dojutsu was extraordinary enough to allow Shinji to barely harness the Rinnegan, preventing it from overpowering him.
After some time, 'Susanoo Tomoshibi' began to take effect. Shinji felt a powerful surge of dojutsu power emanating from the Rinnegan, augmenting his own.
Simultaneously, his mind instinctively grasped two Rinnegan abilities: 'Shinra Tensei' and 'Bansho Ten'in.'
Shinji raised his hand, aiming at a wooden stake in the testing area.
With a bang, the stake's base snapped, and the upper half flew into the air, as if grasped by an invisible hand, soaring toward Shinji.
Catching the half-stake in his palm, Shinji smirked, then activated 'Shinra Tensei,' sending the stake flying back to crash heavily against the wall, shattering into pieces.
Not satisfied with these basic abilities, Shinji activated 'Susanoo Tomoshibi' again, exploring other Rinnegan powers.
He soon discovered he had also gained the ability to absorb chakra.
However, he faintly sensed flaws in this ability, and even in 'Shinra Tensei' and 'Bansho Ten'in.' For instance, using 'Shinra Tensei' required a full fifteen seconds to gather dojutsu power.
He clearly recalled that Nagato's cooldown for 'Shinra Tensei' was only five seconds.
Karin had also tested it; as the Rinnegan's original owner, her cooldown for 'Shinra Tensei' was just over three seconds.
This clearly wasn't an issue with the Rinnegan itself but rather a result of Shinji harnessing a stronger power with a weaker one. Using 'Susanoo Tomoshibi' to access the Rinnegan's abilities caused significant loss.
Fortunately, his primary goal in harnessing the Rinnegan wasn't to boost his combat strength but to use its 'All Creation Power' to nourish his own Eternal Mangekyo Sharingan.