Ayato Uchiha or Tengu Sakai wasn't always the elusive killer the world made him out to be. For long ago he belonged to the most prominent clan within the village known as Konohagakure, the Uchiha. One of many orphans who darkened their doorstep once all other options had been exhausted.  However currently they like all other clans in the world were focused solely on the war. In essence, most adults were absent from the village leaving only a few to nurture the young within the academy. Now Ayato wasn't one for learning, nor did he care to be taught. In fact, he often dozed off in class instead of listening to the teacher's lectures. Although they couldn't do much of anything at the tender age of 6, and so they simply made him clean graffiti off the Hokage statutes as punishment. Something he both enjoyed as it got him out of class, but also left to read books.

With the war persisting Books of myth, and legend were all that Ayato found comforting. Especially given the fact that his home was often empty due to the adults within his clan mostly being gone. The story of winged monks who were seen as deities, and demons by those who heard of them. However, after reading that they were also considered harbingers of war by some religious sects he began to both admire, and despise them. From then on he wandered into the forest behind his home and fed the owls that nested nearby in hopes of appeasing any tengu that may have been lurking in the mountains nearby. By his tenth birthday, he finally saw the end of the wars, but as a result, most of the Uchiha clan perished protecting their clan head the Hokage. Yet she barely survived, and given how she was constantly on the verge of death the village decided to vote for a new leader. But Ayato didn't care. Instead, he chose to focus only on his adoptive mother and did so every day until she died three years later.

Devastated by his lost Ayato retreated into his home remaining isolated from the world as he distracted himself with reading. Yet he only returned in order to attend the graduation ceremony as his mother wished him to. As a genin, he was required to go on missions, but not interact with his squad, who were both heirs to the clans they belonged to. The first Seto Aburame, and the second Yumi Nara. Compared to Ayato they were a pair of happy-go-lucky kids, who didn't seem to have lost anyone in the war. Due to this simple fact alone he avoided them and at least tried to avoid spoiling their peace. An act of kindness Seto took as a provocation, and began to hate Ayato for it. Or at least that was the surface reason. In truth, he'd been more concerned with the fact that Yumi a girl he'd known his whole life was paying attention to the spoiled brat of the dead Hokage.

The first official mission of Squad:Re was supposed to be a simple scouting mission of a mine on the very outskirts of the village. Upon reaching it they weren't immediately ambushed, or attacked by anything. In fact, all they found was a peaceful mine. The villagers who were said to have disappeared were still their working as they should, but something was amiss either way. An air of uneasiness was spread amongst the area, and as they made a plan each of them entered the mine single file. The deeper they traveled the thicker the chakra in the air became, and the more corrupt&toxic it seemed. Upon reaching the center they'd find a group of cultists worshipping a beast of some kind. The others panicked at the sight of it, but Ayato identified it as a Nue. Yet another beast he was quite fond of in terms of the myths he read through. Seemingly they were an omen, and bringers of misfortune.

Their sensei wished to retreat, but Seto had already charged forward in hopes of impressing Yumi. Even as a ninja a mere genin couldn't hope to take on an entire cult, and a nue itself. Terrified for his own life their sensei fled, and Ayato rushed in cutting down two of the cultists that surrounded Seto. After doing so he grabbed Yumi, and fled with both of them. The trio kept running until they reached the village gates. The cultists chased them down and surrounded them by that time as well. Only a few feet away from safety, and still caught up in sudden death. In this instance, the Sharingan he took from his mother's coffin stirred from within the necklace awakening a veil of chakra resembling a technique his mother was known to utilize. The sudden burst spooked their pursuers allowing Ayato to slip inside alongside his squadmates. Once inside the Anbu chased off the cultists, and their sensei who fled was thrown in prison. The village investigated these cultists again, but they'd moved shop by then. Every trace of them had disappeared, but Iwagakure recently took up a new deity who was proposed by their Kage. The village faded from existence shortly after, and in its place, Demonbarē was found.

It would be nearly 8 years after the fall of Iwagakure village at the hands of an unknown cult. Any survivors of the attack could be spotted across the land but were not much help as they were often in a trance-like state upon approach. Almost as if they were going through the motions of life, but not actually living. Because of this, they couldn't give out any information, and many simply assumed it was a Genjutsu that made them that way. Of course, they tried to reverse it, but to no avail. In fact, many died once they were snapped out of the trance, but before doing so they all spoke of the Kage turning into a monkey-like beast before the fell. The Nue. It lined up with the story Ayato had told his own Kage years ago, but went ignored because of the doubt in everyone's minds. As such he was shunned for these years and lived out his days alone. In this spare time, he trained and only made contact with the former members of Squad:Re. However, this was mainly Yumi who simply dragged Seto along with her.

Despite troublesome times they all remained rather close after the incident and rose to the rank of chunin together around the age of 19. Seto now aimed for the Jonin rank while Yumi shifted her eyes onto the medical squads. Whereas Ayato shoved his head into books only to look up for his necessities. It was as if he was obsessed with the idea of slaying mythical beings which many people didn't even believe in. Sure there were talking animals that served as summons, but these were common occurrences. No one had actually come to see a beast of legend before. Nor made contact with them. So many saw him as a madman chasing a futile lead. That is until it happened. "They invaded". A parade of 100 Demons led by the former kage of Iwagakure. The village was not up to the task of defeating these Demons and fell within 3 days. Those that survived were either taken in by the demons as slaves or devoured whole upon being discovered. However, a few managed to escape because of the Sakai.

Yes, an unknown clan descended after the battle if only to save a few orphans. No one else was rescued or even considered. Ayato was one such person, but unlike everyone else, he had killed them. Ayato had managed to kill several Yokai that cornered him, but it came at the cost of Yumi who came to warn him of the invasion. As for Seto he defected over to the side of the Yokai and was granted a place amongst them. Enraged by both events the boy killed a flock of Yatagarasu and a Tengu who led them. A man calling him the Founder of the Sakai clan arrived moments later, and saw what the boy had done. He then performed one of many jutsu rituals to unlock the memories of Ayato from when he was a child and thus granted him back the 15 years he spent training with the Founder as a child. It was later explained that the founder of the Sakai was a member of the Ōtsutsuki clan that would be considered celestial beings in the eyes of those on their planet. He granted the world chakra through a special tree brewed from his own life force, and thus the world of today was born. However with his power also can odd mutations that took the form of Yokai. Chakra demons chased after living beings in order to absorb the chakra they possessed for themselves.

Afterward Ayato officially joined the Sakai clan, and with them, he set out to free humanity from the Yokai menace that was destroying the world.