Uchiha Gen's Mangekyō Sharingan

As the entire Uchiha clan mobilized, leading numerous ninja in purging the remnants of the Hokage faction throughout Konoha.

Uchiha Gen, one of the Uchiha's central figures, was quite relaxed.

He brought Uchiha Fugaku, who had fallen unconscious from Chakra exhaustion, back to the Clan Shrine. After having the clan medical ninja who had just finished treating Uchiha Itachi revive him, he began helping Uchiha Fugaku undergo an eye transplant.

To advance from the Mangekyō Sharingan to the Eternal Mangekyō Sharingan, one needed to fuse the Pupil Power of a blood relative's Mangekyō Sharingan with one's own.

This would elevate Yin Release to its utmost limit.

Only then could one obtain an Eternal Mangekyō Sharingan that would not go blind and whose Pupil Power could recover on its own.

Under Uchiha Gen's watch, Uchiha Fugaku calmly completed the process of fusing the Eternal Mangekyō Sharingan.

He extracted all the Pupil Power from his own Mangekyō Sharingan and merged it back into his brain. From that moment onward, his original pair of Mangekyō Sharingan was completely ruined.

He then replaced them with Uchiha Itachi's pair of Mangekyō Sharingan. The Pupil Power that had receded into Uchiha Fugaku's mind began merging into Uchiha Itachi's Mangekyō Sharingan.

The Pupil Power of the two pairs of blood-related Mangekyō Sharingan fused together without the slightest obstruction, beginning to elevate into the ultimate power of Yin Release.

Ultimate Yin Release would in turn improve one's physical constitution, causing both Chakra reserves and taijutsu to surge dramatically.

This entire fusion process would last three days.

Three days later, Uchiha Fugaku would possess the Eternal Mangekyō Sharingan and attain true Super-Kage-level combat power.

"Gen-kun, I can tell you're in a very good mood. You're even happier than when your own Sharingan Pupil Power advanced."

Temporarily blinded, Uchiha Fugaku