Asura and Indra

Summary
At night, Asura and Indra read about ninshū, Indra effortlessly covering volumes of Hagoromo's writings while Asura struggles. The next day, the two fish together, Indra catching a big fish, and Asura only getting a piece of driftwood. Indra transforms the driftwood into a fish. Indra showcases his talent at manipulating chakra to his father, brother, and other ninshū followers, calling the hand formations used to shape the chakra "seals" and the effects "jutsu". Indra's innovations change ninshū, giving it practical, everyday uses. From the shadows, Black Zetsu observes Indra. Indra shares his concerns about the potential applications of jutsu with Hagoromo, who argues that if Indra had not had such a breakthrough, someone else would have. Indra and Asura spar. Futami mentions to Hagoromo he believes the future of ninshū would be safe under Indra's leadership. Asura goes to play with his friends, who decide to go hunt a wild boar that has been damaging the fields, confident Asura's ninshū will save them if necessary. Having previously only detected its presence, Indra meets Black Zetsu, who talks about a power he can awaken if he loses someone he loves. Indra fears for Asura. Asura and his friends are attacked by the wild boar, which kills their dog Shiro. Asura struggles to perform ninshū, but Indra arrives in time to save him. Asura notices a change in Indra's eyes, which have awakened the Sharingan. Indra confronts Black Zetsu, who tells him to use those eyes to see the truth. Indra grows harsher, more isolated, and more focused on performing jutsu. Black Zetsu continues to influence him.

Trivia

 * Indra's Sharingan is shown fully matured while sparring with Hagoromo's followers, but is later depicted with only two tomoe.