His previous approach had failed because, after repeated attempts, Shinji had discovered that Kimimaro's and Neji's cells simply wouldn't fuse.
At first, he'd thought his Medical Ninjutsu skills weren't good enough.
But as his skill in Medical Ninjutsu improved by leaps and bounds, he realized that not everyone's cells could be perfectly fused.
That was the problem with his "Rinnegan Plan."
The Eternal Mangekyo Sharingan had the ability to neutralize First Hokage cells, so all he had to do was follow the steps and overcome each obstacle one by one.
But the first step of his "Tenseigan Plan" was already impossible.
He didn't know whether there was something wrong with Kimimaro's cells, or whether the Kaguya Clan and the Hyuga Clan weren't as complementary as the Senju Clan and the Uchiha Clan.
In any case,
the Byakugan did have some ability to neutralize Shikotsumyaku, but it was nowhere near as effective as the Sharingan was against First Hokage cells.
It seemed the two simply weren't compatible enough.
"Perhaps Hagoromo Otsutsuki was inherently weaker than the Sage of Six Paths. And unlike Ōtsutsuki Ashura and Ōtsutsuki Indra, he had no descendants like them, so his bloodline became more mixed and less orderly as it was passed down."
After a long period of thought, Shinji reached a conclusion.
After all, the Sage of Six Paths had sealed Kaguya and obtained the Ten-Tails, briefly ascending to the level of a wielder of Kekkei Mōra.
It was only after splitting up the Ten-Tails, founding Ninshu, and sharing Chakra with his students that he fell back to Six Paths level.
By comparison,
Hagoromo Otsutsuki was merely an ordinary Six Paths-level shinobi, clearly half a step below the Sage of Six Paths in strength.
Moreover, the thousand-year struggle between the Sage of Six Paths' two sons,