The previous approach didn't work because, after repeated attempts, Uchiha Shinji discovered that Kimimaro's and Neji's cellular tissues simply couldn't fuse.
At first, he thought it was due to his own limited proficiency in medical ninjutsu.
But as his mastery of medical ninjutsu advanced, he realized that not all cellular tissues could perfectly integrate.
In his Rinnegan Plan, the Eternal Mangekyo Sharingan had the unique ability to neutralize the First Hokage's cells, allowing him to methodically tackle each step's challenges.
But in the Tenseigan Plan, the very first step was a dead end.
He wasn't sure if the issue lay with Kimimaro's cellular structure or if the Kaguya and Hyuga clans lacked the compatibility that the Senju and Uchiha clans shared so seamlessly.
In any case, while the Byakugan did have some neutralizing effect on the Shikotsumyaku (Dead Bone Pulse), it was far less effective than the Sharingan's ability to counter the First Hokage's cells.
It felt as though the two were simply not meant to align.
"Perhaps Hamura Ōtsutsuki's power was inherently weaker than the Sage of the Six Paths. He also lacked heirs like Asura and Indra, so his bloodline's传承 became more muddled and chaotic…"
After much contemplation, Shinji reached a conclusion.
After all, the Sage of the Six Paths, who sealed Kaguya and gained the Ten-Tails, had briefly ascended to the Bloodline Encompassing level.
It was only after dividing the Ten-Tails, founding the Ninja Sect, and distributing chakra to his disciples that he fell back to the Six Paths level.
In contrast, Hamura Ōtsutsuki was merely an ordinary Six Paths-level figure, clearly half a tier below the Sage of the Six Paths in strength.
Furthermore, the millennia-long conflict between the Sage's sons, Asura and Indra, was one of the root causes of the shinobi world's endless wars. However, it also solidified the strong compatibility between the Senju and Uzumaki clans, who inherited the Sage's body, and the Uchiha clan, who inherited the Sage's dojutsu power.
Meanwhile, the Kaguya clan, who inherited Hamura's Sage Body, and the Hyuga clan, who inherited Hamura's Sage Eyes, saw their bloodlines grow increasingly diluted and less compatible over a thousand years of propagation, unable to match the synergy of the Senju, Uzumaki, and Uchiha.
Thus, whether it was enhancing Neji's physique with Kimimaro's cells or boosting Kimimaro's dojutsu power with Neji's Byakugan, both were nearly impossible with Shinji's current techniques.
This was the greatest obstacle stumping Shinji!
He lacked a host like Toneri Ōtsutsuki, who possessed both a perfect physique and exceptional dojutsu power to awaken the Tenseigan.
The candidates he had initially pinned his hopes on—Neji and Kimimaro—were, in truth, unqualified as hosts for awakening the Tenseigan.
Scritch, scritch.
Shinji crossed out Neji's and Kimimaro's names in his notebook, letting out a faint sigh. "Ugh, am I really forced to target Toneri Ōtsutsuki?"
But if Toneri awakened the Tenseigan, his power would skyrocket to near-Six Paths level. At that point, Shinji wasn't even sure he could defeat him.
After all, in the original timeline, Toneri had the feats of effortlessly overpowering Naruto post-Fourth Great Ninja War.
If it weren't for Naruto and Hinata teaming up to destroy the Giant Tenseigan, even Naruto—at the time arguably the strongest in the shinobi world—wouldn't have been able to defeat Toneri.
Using Toneri as a host would be sheer madness.
"How can I combine Kimimaro's and Neji's strengths?"
Closing the notebook, Shinji leaned back in his chair, twirling his pen.
Suddenly, a spark of inspiration flashed in his mind.
He couldn't transplant Kimimaro's cells into Neji or Neji's Byakugan into Kimimaro, but that didn't mean he couldn't create something akin to a White Zetsu—a biological exoskeleton that could attach to a person!
Whoosh!
He shot to his feet, pacing back and forth in the cramped laboratory.
This bold idea instantly cleared his mental fog. He didn't need to achieve complex cellular fusion at all. He only needed a biological exoskeleton capable of hosting both Kimimaro's and Neji's powers, acting as a bridge to merge their strengths!
As for the host for awakening the Tenseigan, it didn't have to be limited to a single person.
The Giant Tenseigan on the moon had already given Shinji his greatest inspiration: the Tenseigan was highly inclusive!
Thus, both Kimimaro and Neji could be hosts. Even the biological exoskeleton created for them could be considered a host for awakening the Tenseigan.
Returning to his seat, Shinji flipped open his notebook and began writing furiously.
From conceptualization to execution, he outlined an entire plan.
First, he needed to create a biological exoskeleton capable of simultaneously accommodating Kimimaro's and Neji's chakra.
No!
His gaze sharpened. This biological exoskeleton also needed to be compatible with his own chakra.
When the time came to awaken the Tenseigan, he might need to use Jikibi and Wazunagi to extract chakra, so the exoskeleton had to accommodate his chakra as well.
Pausing his pen, he mused, "If that's the case, the cellular structure of this biological exoskeleton could be based on my own!"
Neji's body couldn't fuse with Kimimaro's cells, but that didn't mean Shinji's couldn't.
Besides, fusing a biological exoskeleton was different from direct implantation into a body—it would be less challenging overall.
Moreover, his chakra was already at an exceptionally high level.
Using his own cellular structure as the foundation for the biological exoskeleton could also stimulate Kimimaro's and Neji's chakra.
Shinji resumed writing.
He began outlining a plan for a biological exoskeleton with his cellular structure as the primary component, supplemented by Kimimaro's and Neji's cells.
In his vision, once this biological exoskeleton was complete, he could have Kimimaro and Neji wear it long-term to establish a connection between the exoskeleton and their bodies. Ultimately, through chakra channels created by Jikibi and Wazunagi, the chakra of all three could be fused together.
Of course, this concept still had many areas that needed refinement and optimization. But at the very least, Shinji now had a direction to pursue, rather than being stalled by Neji's inability to fuse with Kimimaro's cells, forcing him to shelve the Tenseigan Plan.
At the same time, he faintly realized that the biological exoskeleton could serve as a chakra transfer hub for Wazunagi. Once completed, he would no longer need to worry about where to channel the extracted chakra.