In the anime, despite the loss of his mother following problems with his younger brother Asura's birth, Indra's childhood was still peaceful and joyous, spending his time either blissfully alongside his father and brother Asura, or regularly reading his father's books and journals. Under their father's tutelage, the two brothers studied Ninshū in the hopes of one of them becoming the great sage's successor. As Indra continued to amaze all with his natural capacities and advanced growth rate, he began showing his ingenious side, realising how chakra could be altered to perform more versatile feats. Soon afterwards, the other Ninshū followers learned from Indra's example and began using this new innovation to improve the quality of life. While initially proud of his discovery, Indra grew concerned when he noticed that everyone began focusing more on physical growth rather than spiritual as what was meant for Ninshū. Periodically, Black Zetsu would approach Indra alone, goading him with praises and curiosity towards Indra's true potential, even going so far as to say he could rival if not surpass the Sage of Six Paths himself. After awakening his Sharingan, Indra began to take to heart the mysterious figure's praises, focusing solely on his training and growing colder to others, including his brother. Eventually, Hagoromo decided to choose his successor based on the performance of his sons by tasking them each with aiding the revival of a foreign land.
Upon arriving at his destination, Indra learned that the land was in reality very fertile due to the existence of a God Tree sapling; however, he also realises that it caused the people there to gradually grow sick from relying on its nutrients. Deciding to resolve things quickly, Indra used his Sharingan to force the villagers to destroy the sapling and discover water. Upon returning home, Indra was surprised that Hagoromo chose to wait for the return of Asura as well before making his decision for successor. While respecting his father's wish, Indra grew restless, something that Black Zetsu picked up in another meeting, noting that Indra's vision of the future differed from Hagoromo's. A year passed since the two brother's received their respective mission, and Indra continued training others, starting again to appreciate the company of people. Eventually, Asura returned, but with many people from the village he was sent to who helped him complete his mission. Asura then met with his brother to hear Hagoromo's final decision.
When their father chose Asura carry on his dream of establishing peace throughout the world, Indra was enraged that his younger brother was chosen over him and more so that his father noted Indra's inability to acknowledge others while focusing on power as a factor in his decision. While Hagoromo tried to reason with Indra, noting that the village he "helped" had ultimately destroyed itself after he left due to the villagers recklessly fighting over the water, his words fell on deaf ears. In the anime, growing so bitter towards his family while simultaneously revelling in his growing power, he came to view his father's ninshū as incomplete and cowardly, wanting to change it into ninjutsu to reflect his views of using power to create peace and order. Wanting to ensure he was powerful enough to challenge his father and brother, he killed his two closest friends to awaken the Mangekyō Sharingan. On the night of Asura's celebration as the successor, Indra attacked the village, voicing his disdain for his family and ninshū, insisting that ninjutsu was superior and the true means for peace. With sadistic joy, he attacked Asura, who surprised the older brother with his growth in repelling the attack. Determined to crush his brother and take his desired position as the true bringer of peace, Indra unleashed his Susanoo. While Asura was able to hold his brother off, having manifested his newfound power passed on to him from Hagoromo, Indra's massive construct began overwhelming him. Hagoromo then had the village all share their chakra with Asura, allowing him to fully manifest his powers and unleash the Wood Release. Combining this with the Six Paths Senjutsu, Asura was able to defeat Indra who, still refusing to acknowledge his brother, was forced into retreat. Years later, Indra went into hiding and formed a sect that supported ninjutsu. As Hagoromo was rendered bedridden as he neared the end of his life, Indra approached his estranged father, boldly telling him that his cowardly approach to peace would only bring about greater wars, which Indra would take advantage of to destroy ninshū, vowing to do so in as many reincarnations as necessary.