The more Shinji thought it over, the more excited he became.
As the central figure in his "Rinnegan Plan," Karin's strength was key to whether the plan could succeed.
To raise the plan's chances of success, Karin's Yang Release Chakra and Yin Release Chakra both had to reach their absolute limits!
As for Yin Release Chakra...
If Karin could recover those two completely damaged Mangekyō Sharingan this time, Shinji would have at least a thirty percent chance of helping her fuse them into an Eternal Mangekyo Sharingan.
It still wouldn't be the absolute limit, but it would at least meet the threshold for attaining the Rinnegan.
As for Yang Release Chakra...
As a member of the Uzumaki Clan with a healing constitution that was extremely rare even among her clan, Karin already possessed powerful Yang Release Chakra.
On top of that, the White Zetsu Cell transplant Shinji had performed on her earlier had further improved the quality of her Yang Release Chakra.
At this point, she had basically reached the limit.
If he wanted to increase her Yang Release Chakra any further, directly transplanting First Hokage cells was the only way.
After all, White Zetsu Cells were the product of Madara Uchiha using the power of the Divine Tree to dilute First Hokage cells.
Put simply, White Zetsu Cells were a downgraded version of First Hokage cells.
Their power had been sacrificed to improve the transplant's success rate and make them easier to control.
If Tsunade hadn't been performing Yakumo's surgery this time, Shinji wouldn't have dared to transplant First Hokage cells into Karin.
But if Tsunade succeeded, he could follow her example and reproduce the surgery on Karin, further increasing the chances of the "Rinnegan Plan" succeeding.
I really did make the right move!
He secretly rejoiced.
Getting Yakumo