Asura Ōtsutsuki

was the youngest son of Hagoromo Ōtsutsuki and heir to his teachings. He is also the ancestor of the Senju clan, as well as the Uzumaki clan.

Background
As a child, Asura lived in his genius brother Indra Ōtsutsuki's shadow in every conceivable way, having displayed no natural talent himself. Because of this, Asura came to realise the value of others and their power of the many friends and allies he made before eventually awakening his own power which equalled that of Indra's.

On his deathbed, Hagoromo selected Asura to carry on his dreams of peace for the world. Indra, believing that he should have been chosen, fought Asura to try and claim what he felt should have been his birthright. Both brothers went to their graves constantly fighting over the title of the successor of Ninshū, but not before leaving behind offsprings who would continue the battle for centuries to come. Indra's descendants — who would become the Uchiha clan — would continue this fight with Asura's descendants — who would become known as the Senju clan — never knowing why or how their hatred of each other came to be.

Personality
Asura believed that love was the ultimate key to peace, and loved his father greatly as well. Though the son of the famed Sage of the Six Paths, Asura was born with practically no talent, but because of this, he learned the value of depending on and cooperating with others. Asura adored Indra he would constantly devote himself to studying, aiming to be like his older brother. Through sheer hard work and determination, he was able to awaken his own power. Because he never lost sight of the value in people, he would ultimately become the successor to his father's Ninshū as Hagoromo wanted the world to adopt this 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, and also had stern facial features. He also wore what seemed to be a blank forehead protector and at a later time, bandages around his forehead. He wore a light-coloured kimono which was adorned with magatama around the collar. The kimono was held closed by a dark-coloured sash. Underneath all of this he wore a black full-body suit.

Abilities
As a child, Asura was considered to be unskilled, much unlike his genius older brother, Indra. Over the years however, through gruelling hard work and dedication, Asura came to obtain might rivaling his brother's and proving himself a late bloomer, awakening his own inherit power, his father's "body": powerful life force and physical energy. He also became a capable leader, obtaining countless loyal followers. It was because of Asura's philosophy that caused his father to bless him with his power and grant him succession of 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 utilise Six Paths Senjutsu to enhance his abilities, become able to fly, as well as manifest a giant three-headed, six-armed battle avatar. This avatar was capable of going head to head with Indra's Complete Body — Susanoo.

Truth-Seeking Balls
Asura had the ability to manifest at least five large Truth-Seeking Balls, which are 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 also seen wielding a shakujō, as well as a sword on different occasions.

Legacy
Hagoromo noted that Asura's chakra remained even after his body was destroyed, and it was reincarnated in various individuals throughout history who all inherited his will as well as the chakra and powers his body once held. His prior reincarnation being Hashirama Senju. When Madara Uchiha, the reincarnation of Indra of Hashirama's time, his power hungry way has led him to forcefully obtain Hashirama's DNA and implant it into his own body, thus, a portion of Asura's chakra, and the two have resulted in Madara awakening the Rinnegan. When Hashirama and Madara died, the transmigration circle resumed, and Naruto Uzumaki became the current inheritor of Asura's will.

Asura's ideals also allowed his father to realise a new possibility for the world, and with this he used the Creation of All Things to separate the Ten-Tails' chakra into nine tailed beasts, gave each of them names, in the hopes that when the time came, they would to be reunited as a single entity, yet not as they originally were, and that one shall appear at that time to show them what true power is. The beasts would come to believe this individual to be Naruto centuries later.

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

Ultimately, it was Asura's latest reincarnation, Naruto Uzumaki who managed to do what all of his prior incarnations had failed to do: end the rift created by the two lines of the reincarnated brothers, which Naruto achieved by defeating Indra's successor, Sasuke Uchiha, in their final battle, finally bringing about the end of the bitter feud that had lasted for centuries.

Trivia

 * The rivalry of Indra and Asura and their descendants (Uchiha and Senju) is derived from Hindu and Buddhist religions where the Gods, led by Indra, are in constant battle against the Asuras. Although the Asuras were malevolent, and the Gods benevolent, here the roles are reversed.
 * His battle avatar is befitting of his name, as Asura are often depicted as belligerent beings with three faces and six arms much like the Asura Path of the Rinnegan as it is depicted 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.