Asura Ōtsutsuki

was the younger son of Hagoromo Ōtsutsuki and heir to his teachings. He is also the ancestor of both the Senju, and the Uzumaki clans.

Background
As a child, Asura lived in the shadow of his genius older brother Indra Ōtsutsuki. Having displayed no natural talent himself, Asura came to realise the value of others and the power of the friends and allies he made. Eventually, he awakened his own power which equalled Indra's power.

On his deathbed, Hagoromo selected Asura as his successor to carry out his dream of peace & understanding in the world. Indra, believing that he should have been chosen instead as it was his birthright, was manipulated into fighting Asura. Both brothers died fighting over the title of the successor of Ninshū, but not before having offspring who would continue this feud for centuries to come. Indra's eventual descendants — the Uchiha clan — would feud with Asura's eventual descendants — the Senju clan. Neither clan knew why or how their hatred of the other came to be.

Personality
Though the son of the famed Sage of the Six Paths, Asura was born with no talent and thus could not accomplish much on his own. Instead, he valued depending on and cooperating with others. Asura adored Indra and would constantly devote himself to studying, aiming to be like his older brother. With the help of his countless friends and allies, and through sheer hard work and determination, he awakened his own power. As he never lost sight of his principles and the love he had for others, he believed love to be the key to peace. This ultimately convinced Hagoromo to anoint Asura as the successor to his Ninshū as Hagoromo wanted the world to adopt Asura's way of thinking.

Appearance
Asura had short, spiky brown hair — two locks of which were wrapped in bandages framing either side of his face in a similar manner to his brother. He possessed stern facial features. He wore what seemed to be a blank forehead protector and at a later time, bandages around his forehead. He wore a light-coloured kimono with magatama adorned around the collar. The kimono was held closed by a dark-coloured sash. Underneath, he wore a black full-body suit.

Abilities
A late-bloomer, Asura was considered to be unskilled, unlike his older brother Indra, who was a genius. Over the years however, through gruelling hard work and dedication, Asura awakened his own inherited power: his father's "body" — powerful life force and physical energy. He was also a capable leader, obtaining countless loyal followers. It was because of Asura's philosophy that his father blessed him with his power and made him the successor to Ninshū.

Six Paths Sage Mode
With the power entrusted to him by his father, Asura gained access to the Six Paths Sage Mode. In this state, he could fly, and his abilities were enhanced by Six Paths Senjutsu. He could manifest a giant three-headed, six-armed, battle avatar, which he used to combat Indra's Complete Body — Susanoo.

Truth-Seeking Ball
Asura had access to least five large Truth-Seeking Balls, which were composed of the five basic nature transformations, Yin–Yang Release, and Six Paths Sage Chakra. In battle, he would make use of them in conjunction with his battle avatar.

Bukijutsu
He was seen wielding a shakujō, as well as a sword on different occasions.

Legacy
Though his body was destroyed, Asura's chakra would continue to exist. His chakra reincarnated into various individuals throughout history, and his reincarnations would also inherit his will.

During the Warring States Period, Hashirama Senju was his reincarnation. Hashirama possessed what the people of Konoha called the Will of Fire, which many people believed in. With the help of Madara Uchiha, the reincarnation of Indra at the time, Hashirama created the very first ninja village, Konohagakure, and helped set up the ninja system. However, Madara would defect, and resumed his conflict with Hashirama. When Hashirama and Madara died, the transmigration circle resumed. Naruto Uzumaki became the latest inheritor of Asura's chakra & will, with Sasuke Uchiha inheriting Indra's chakra & will.

Asura's ideals enabled his father to realise a new possibility for the world. Hagoromo created the nine Tailed Beasts by using Creation of All Things to separate the Ten-Tails' chakra. He gave each of them names, in the hopes that when the time came, they would be reunited as a single but different entity, and that at that time, a person would appear who would show them what true power is. When Naruto befriended them centuries later, the beasts came to believe that Naruto was this person.

Ultimately, Naruto managed to do what all of the previous reincarnations had failed to do: end the rift between the two lines of the reincarnated brothers. Naruto achieved this after defeating Sasuke, who finally accepted Naruto's ideals at the end of their fight. This brought about the end of the bitter feud that had lasted for centuries.

According to Black Zetsu, the reincarnations of Indra and Asura were almost always in conflict with each other and rarely worked together. Naruto and Sasuke are one of the exceptions, assuming other exceptions have existed throughout the centuries.

Trivia

 * The rivalry of Indra and Asura, and their descendants (Uchiha and Senju), is derived from Hindu and Buddhist religions. The Gods, led by Indra, are in constant battle with the Asuras.
 * His battle avatar is befitting of his name, as the Asura are often depicted as belligerent beings with three faces and six arms. The Asura Path is depicted in the same way.
 * As Asura believed that love was the key to peace, it is possible that Hashirama Senju's "Will of Fire" evolved from his beliefs. Similarly, his brother's descendants rose to oppose this, inheriting the "Curse of Hatred".
 * Like his father, Asura mainly wielded a shakujō in battle. His choice of weapon could represent his desire for love and peace, while his brother's choice of a sword could symbolise his lust for power.
 * Through the use of shadow clones while using his Tailed Beast Mode and Six Paths Sage Mode, Naruto Uzumaki was able to combine three of the avatars into a single, three-headed, six-armed construct similar to the one Asura used in the past.