The plan for the fusion surgery had been rehearsed countless times in Uchiha Shinji's mind, so despite it being his first time performing it, he moved with no trace of hesitation.
Disinfection.
Incising the eye socket.
Implanting the Mangekyo Sharingan.
Injecting the fusion agent.
Cleaning and suturing the wound.
The entire procedure flowed seamlessly under Shinji's hands.
In less than three minutes, he completed the process—from cutting open the transplant site, implanting the second pair of Mangekyo Sharingan, to the final cleaning and suturing.
Finally, he carefully wrapped Karin's eyes with bandages, replicating the appearance of the wound treatment she received at the hospital.
This way, even if Jiraiya visited again, he wouldn't notice anything amiss!
After tidying up, Shinji packed away the surgical tools and asked Karin, "How do you feel right now?"
Karin thought for a moment before saying, "A bit swollen."
Shinji blinked. "Just swollen?"
Still lying on the bed, careful not to move, Karin nodded slowly. "Yes, no pain or itching for now—just a slight swelling sensation."
"Logically, the influx of new dojutsu power should cause palpitations, maybe even some slight stinging," Shinji mused, resting his chin in his hand.
Thanks to Susanoo Tomoshibi, if Shinji claimed to be the second-best in the shinobi world at eye fusion, no one would dare claim first.
Coupled with his recent intensive study of medical ninjutsu, he could extrapolate many surgical techniques.
According to medical ninjutsu theory and Shinji's own understanding of dojutsu kekkei genkai, fusing two pairs of Mangekyo Sharingan from unrelated bloodlines should cause palpitations, stinging, or even splitting headaches.
Yet Karin only felt mild swelling, which suggested one thing: the rejection between the two pairs of Mangekyo Sharingan was minimal.
"My plan might actually succeed!"
In that moment, Shinji's confidence in his Rinnegan Plan soared.
Karin suddenly asked, "Leader, how long will the fusion take? Iruka-sensei only requested half a month's leave for me."
"Half a month should be enough," Shinji replied, pausing before adding, "Even if it's not, it won't be far off."
How long it took Uchiha Madara to fuse his Eternal Mangekyo Sharingan was impossible to verify now, but Shinji knew Sasuke had taken about a month to recover in Obito's secret base.
Karin said, "If half a month isn't enough, I'll have to ask Iruka-sensei to extend my leave by another week."
"Don't worry about that now. Focus on facilitating the fusion. I'll handle the rest!" Shinji instructed.
As long as powerhouses like Tsunade or Jiraiya didn't catch on, Shinji was confident he could deal with anyone else who noticed something.
"Understood!" Karin replied, visibly relaxing.
Watching Karin on the bed, Shinji began analyzing which two dojutsu the fused Eternal Mangekyo Sharingan would retain.
The fully damaged Mangekyo contained Amaterasu and Kagutsuchi, while the partially damaged pair held Susanoo Tomoshibi.
Though Susanoo Tomoshibi had different effects in each eye—one reducing Susanoo's chakra consumption, the other enhancing its power—it was akin to Obito's Kamui, still considered a single dojutsu.
Thus, the two pairs of Mangekyo collectively held three dojutsu: Amaterasu, Kagutsuchi, and Susanoo Tomoshibi.
Since the fusion wasn't performed with Susanoo Tomoshibi, the resulting Eternal Mangekyo Sharingan could retain at most two dojutsu.
"Three choose two, huh?" Shinji's eyes flickered.
Because it could counter spirits, Amaterasu earned bonus points in Shinji's view.
But Kagutsuchi was different. This shaping dojutsu was, in Shinji's opinion, only useful against weaker opponents. Against strong foes, its effectiveness dropped significantly.
As for Susanoo Tomoshibi, if Karin successfully fused the Eternal Mangekyo Sharingan, the ability to reduce Susanoo's chakra cost would be redundant, given her robust Sage Body and the immense dojutsu power of the Eternal Mangekyo. It was practically useless.
The ability to enhance Susanoo's power was also somewhat lackluster.
After all, the Eternal Mangekyo Sharingan could already manifest a Perfect Susanoo. Unless Susanoo Tomoshibi's enhancement could push Susanoo beyond the Perfect form's limits, it wasn't particularly valuable.
But if it could surpass that limit, the ability was worth keeping.
"The optimal choice is to retain Amaterasu and the part of Susanoo Tomoshibi that enhances Susanoo's power."
Having reached this conclusion, Shinji didn't rush to discuss it with Karin.
First, he wasn't sure if Karin could consciously choose which dojutsu to retain during the fusion process. Second, the surgery had just been completed, and Karin, as the host, needed time to rest and adapt. If he were to bring it up, it would be better to wait a few days until her condition stabilized.
After packing up the surgical tools, Shinji left Karin's apartment quietly, not disturbing her recovery.
Soon, he returned to his own apartment.
Shedding his Akatsuki disguise, he sat at his desk, outlining the next steps of his plan.
With Karin now beginning the fusion of the Eternal Mangekyo Sharingan, if successful, she would effectively become the original owner of this new pair.
The Eternal Mangekyo Sharingan component would then be complete.
Next, transplanting the First Hokage's cells into Karin to further elevate her Yang Release chakra would fulfill the First Hokage's cells component.
"Once these two steps are done, the basic conditions for awakening the Rinnegan should be met," Shinji muttered, scribbling and sketching his action plan in a notebook. But his pen suddenly paused.
The Eternal Mangekyo Sharingan and the First Hokage's cells were indeed the foundational requirements for awakening the Rinnegan. But what if, even after meeting these conditions, the Rinnegan didn't awaken? Or what if, like Uchiha Madara, it took decades of grueling effort to awaken it?
This doubt crept into Shinji's mind, causing his brow to furrow unconsciously.
But soon, his expression relaxed. "There's no point dwelling on this now. The ship will find its way to the bridge. As long as I take each step carefully and steadily, I refuse to believe I can't produce a pair of Rinnegan!"
Besides, Karin was merely a rehearsal for his own attempt at the Rinnegan. His own conditions were even more suited for it than Karin's, so he had little to worry about.