This story began in a place that was previously a mountain but now resembled an unholy offspring of desert and basin. One with good eyes could barely make out green of forest in distance, so great was the destruction and so dense was the dust-haze.
Lying face down in center of now-gone mountain, were two men. Both of them appeared quite dead and void of life.
Suddenly one of the corpses resumed breathing and not a second later struggled to sit up. Inside of the once empty body, strong chakra begin to flow. Chakra that was very similar, some might say even identical, to the chakra possessed by the original owner of that carcass.
The body thief slowly stood up and looked around. After a second his brows frowned in disappointment “tch, Mutual murder in bygone-mountain. So sacrificing Rinnesharingan only throw me back three century.” He was quite upset he couldn’t nip that creature in the bud. Still three centuries meant two century before "his" birth. It wasn’t too late. As long as he stopped Zetsu now, maybe fighting would became less intense and "he" would live to old age.
He resolutely didn’t let himself consider that changing future might lead to none of his siblings being born.
After forcefully patching the body up using Chakra, so it would not fail him for the next few hours, he set off. Finding that slimy shadow was as easy as breathing.
He didn’t waste time on reconnaissance or surveying the area. He was both highly confident in himself and quite short on time. With an optimistic estimate he had four hour and with a pessimistic estimate only one hour before this body completely shut itself down. Considering luck is ever a fickle companion going with pessimistic one is more rational. Even so his brazen way of collapsing half of a building and calling black Zetsu out with a war cry is something only he could get away with.
Both half of black Zetsu slithered out of collapsed structure.
“You… How are you still alive? How do you know us?” asked one half of black Zetsu. He was quite sure he felt both of incarnations die together again.
The other one was looking nervously back at the heap of rocks and barely standing structure.” Brother, the experiment…” He was quite worried.
“We will take care of it later. Don’t worry.”
The walking (soon to be a real) corpse didn’t play with them. For once in his life he didn’t use less power for a longer period of dancing. He forced his chakra to activate Rinnegan on his nearly sightless eyes. His eyes started to deteriorate with alarming speed.
He lifted his arm and two half of black Zetsu were elevated into air. Rocks started to gather around them, encasing them into circular prison. The prison moved toward the-one-who-should-be-dead.
He placed his hand on the prison. Lines moved out of his hand and made a shape similar to Rinnegan on the rocks. He said with a smirk.” Rinnegan seal. Go and spend rest of eternity with your precious mother.” The heaps of rock began to move upward and within a couple of meters its momentum was so high that in a couple of more second it vanished from sight.
He silently stood still and watched the rock rise higher and beyond even his considerable sight.
When he could no longer see it, he sighed and closed his eyes. Tension slowly drained his body and he began to let go of his hold on his body. “This time, without Zetsu…”
He didn’t get to finish his sentence. The once and again corpse fall down on ground.
A few Hour later
“Found Him.” Someone shouted. He was clad in Uchiha war robe and looked just like another uchiha.
His squad who also had classic Uchiha looks, gathered together.
“Brother” one of them screamed and rushed forward. Hugging his corpse. His eyes started to water and his sharingan changed shape.
“Why did clan head came here before his death?” one of younger member of squad asked, he pointed at half-destroyed building. “What’s inside there?”
Oldest member of squad nodded toward building. “You four, check out that building. Gather anything that looks important, we will take it back to clan, then demolish the building. I will stay as a lookout.” They went and left him and the-soon-to-be-clan-head alone.
Squad leader looked at his new clan head’s sobbing figure and stayed silent. He could understand all too well how he felt.
His weakened eyes could testify to that.
“Sir” one of squad mate returned. “You need to see this” and thrusted a scroll to his face.
He glared at him and said.” Give it politely, stop thrusting to my face.” And snatched the scroll.
“Experiments on sharingan?” he said unbelievingly.
“Not only on sharingan but also on human body and seals and many other things. There is a wealth of knowledge there. This scroll is special though. There is a theory there about saving eyesight after getting mangekyou sharingan.”
Squad leader started to read. “Fascinating.” He looked at weeping brother who hugged his dead older brother and said. “And easy enough to test.”