Background
Alongside Hamura, Hagoromo, the older twin brother, was born as one of the two children to Kaguya Ōtsutsuki, a princess who ate the forbidden Chakra Fruit of the God Tree that appeared once a millennium in an effort to gain divine abilities, which she used to put an end to the constant wars during that era. As a result, Hagoromo was born with the ability to manipulate the same type of powerful chakra as his mother. Angered by the fact that her chakra had been spread to others, Kaguya merged with the God Tree into the Ten-Tails, which attempted to reclaim her chakra.
The Ten-Tails rampaged throughout the lands until Hagoromo and his brother managed to defeat the beast, with Hagoromo becoming its jinchūriki, causing him to be revered as a god for the virtue of his victory. Researching his mother's technique, Hagoromo was able to free the world from her Infinite Tsukuyomi. Later, with his knowledge of the concept of chakra, Hagoromo travelled across the land, giving chakra to every one in the world as well as spreading his ideals and religion, ninshū, which eventually became the ability known as ninjutsu. According to Jiraiya, his great deeds and ultimate desire to bring peace to the war-torn world made him widely known as the Saviour of this World.
Hagoromo's ultimate wish was to establish peace across the world, but it was a goal that would never be achieved in a single lifetime. Knowing this, he chose to entrust his dream and legacy to his two sons, and began to teach them ninshū. The older son, Indra Ōtsutsuki, was acknowledged by Hagoromo as a true prodigy, who quickly began to revel in his natural prowess and became very solitary. The younger son, Asura Ōtsutsuki, proved to be the exact opposite, having shown no special abilities or natural talent, but he pushed on through his limitations, growing stronger and more mature because of his struggles and making friends with others along the way. Hagoromo acknowledged Asura's chosen path, agreeing that love and cooperation were the true keys to peace.
Inspired by his younger son, Hagoromo separated the Ten-Tails' chakra within his body and used his Creation of All Things Technique to divide it into nine separated bodies, creating the tailed beasts and giving each a name. As a result of extracting them all at once, Hagoromo was left weakened and incapacitated for several months, though the powerful life force of the Ten-Tails' husk kept him alive. Some time after their creation, the young tailed beasts were told that they were all still linked to one another despite being separate entities. Hagoromo also told them that they would eventually become one again, yet not as they originally were, and that one shall appear at that time to show them what true power is. Hagoromo eventually sealed the husk of the Ten-Tails within the moon. On his deathbed, he chose Asura to be his successor, but Indra, overcome by bitterness and envy as well as being encouraged and manipulated by Black Zetsu, fought against his brother, beginning a war between them that would continue through their descendants.
Suspecting that Indra or one of his reincarnations would eventually attempt to take Asura's power for themselves, Hagoromo left behind a tablet detailing his history in an attempt to make them reconsider. Only those who possess the Rinnegan can fully decipher the contents of the tablet, while a reader with other dōjutsu such as the Sharingan can still partially interpret the information. However, unknown to him, Black Zetsu, a manifestation of his mother's will, had altered the contents of his tablet so he could manipulate Indra's descendants, the Uchiha clan, through the ages into resurrecting Kaguya and initiating the Infinite Tsukuyomi anew. Even though Hagoromo died and his body was destroyed, his chakra and consciousness remained and traversed the world throughout the centuries.
Hagoromo and his brother lived in ignorance of their mother's true amoral nature. While their homeland continued to prosper, people would periodically disappear for a sacred Ritual of the God Tree. One day, the brothers were approached by Gamamaru, who revealed to them that beyond the peak of the nearby mountains lied the truth of the ritual. While initially ignoring the toad's words, Hagoromo grew distressed when a local girl he cared for named Haori became part of the ritual. When the brothers confronted their mother about ending the rituals, Kaguya dismissed their concern, simply saying it was necessary for "the others' arrival". Finally deciding to investigate, the two brothers were horrified to learn that the missing citizens were sacrificed to the God Tree. This especially hurt Hagoromo, and he awakened the Sharingan in his grief. Wishing to learn more, the brothers sought out Gamamaru. He revealed to them their mother's history of coming to Earth and using the God Tree's fruit to gain great power and enslave much of the land using Infinite Tsukuyomi, including their father. Deciding that they needed more power to confront Kaguya should she turn hostile, Hagoromo began training under Gamamaru in senjutsu. While Hagoromo quickly improved in this art, Kaguya soon caught on to her sons' scheme.
After Hagoromo completed his training under the Toad Sage, he returned to confront Kaguya, but not before being presented by Gamamaru with a special seal tag instilled with great sage power refined over the centuries. Once approaching Kaguya, the mother and son made their respective views known. As Hagoromo tried to reason with Kaguya, his words fell on deaf ears, as Kaguya deemed Hagoromo as ungrateful. She then had Hamura, who she brainwashed, attack Hagoromo. Unable to reason with Hamura, Hagoromo was left with no choice but to strike down his beloved brother, which awakened his Mangekyō Sharingan and Rinnegan. Deciding to use Gamamaru's one-use gift, Hagoromo placed the seal tag on Hamura and healed him.
Angered by the fact that her chakra had been used against her, Kaguya wills the God Tree to transform into the Ten-Tails, which attempted to reclaim her chakra for her. Hagoromo and Hamura fought both their mother and the Ten-Tails in a battle that lasts for months, decimating the land in the process, until they were able to defeat them both by sealing Kaguya, and Hagoromo split the Ten-Tails' chakra into the nine tailed beasts. Later, Hagoromo was able to free the world from Kaguya's Infinite Tsukuyomi. While Hamura decided to stay on the moon to keep watch of their mother, Hagoromo chose to travel the earth to find proper dwellings for the tailed beasts and repent for the damage he caused the world from his fight against Kaguya. Before leaving, Gamamaru told Hagoromo a prophecy he had about a mischievous blue-eyed child who would one day connect with the tailed beasts and bring about a miracle.
Afterwards, Hagoromo eventually returned to his home village to act as the centre for the teachings of ninshū. He also fell in love and married a woman with whom had two children, Indra and Asura. During the second pregnancy, their were complications as Hagoromo's wife passed not long after giving birth to her second child. Hagoromo later began instructing his sons in Ninshū. The older son, Indra, was acknowledged by Hagoromo as a true prodigy, quickly began to revel in his natural prowess and became very solitary, unaware that much of this came from the subtle manipulations of Black Zetsu. The younger son, Asura, proved to be the exact opposite, having shown no special abilities or natural talent, but he pushed on through his limitations, growing stronger and more mature because of his struggles and making friends with others along the way. Finally deciding the time had come to chose a successor to Ninshū, Hagoromo sent each on his sons on a different mission of restoration for a struggling land that was ravaged by the battle against Kaguya to test their capacities. A year went by since the missions were given, Indra quickly returning after completing his while Asura took much longer. Deciding to wait for his younger son's return before making his decision, he was told the nature of how Indra completed his mission by Gamamaru. Eventually, Asura completed his mission, but also returned with many people from the village, who were inspired by Asura and even learned Ninshū from him, having helped him complete his mission.
With Asura and Indra present, Hagoromo decided to choose his successor in Ninshū. Much to everyone's surprise, Hagoromo chose Asura. This greatly angered and confused Indra, who thought he was worthy of becoming the successor, and he stormed out into the wilderness. Later on, Hagoromo explained to Asura why he chose him as his successor and asked Asura to take care of the world with Indra, and Hagoromo gave Asura his power. Subsequently, Indra in a fit of rage attacked Hagoromo, Asura and the rest of the villagers with his Susanoo and newly acquired Mangekyō Sharingan, with his explanation as to how he obtained the dōjutsu drawing Hagoromo's disgust. Hagoromo and the rest of the villagers transferred their chakra to Asura to help him take on Indra, forcing the elder brother to flee.
