WRITTEN BY RIYA DUBEY
Indra and Ashura are sons of Hagoromo Ōtsutsuki. Indra is the first-born whilst Ashura is the second-born. Indra is considered the creator of Ninjutsu and is the progenitor of the Uchiha clan.
Ashura on the other hand is just as strong as his brother and is said to be the progenitor of both the Uzumaki and Senju Clan.
Indra was supposed to be the inheritor of his father's teaching because of his right as the firstborn, but Hagoromo chose Ashura instead. As a result of this rivalry, the two brothers fought each other bitterly.
Indra wished to rule the entire world and he reincarnated in a different body to fulfill that dream of his. Ashura wished to stop his brother from harming people and he reincarnated to do that.
Indra reincarnated as Uchiha Madara and Ashura Reincarnated as Hashirama Senju. The other reincarnation is Uchiha Sasuke and Uzumaki Naruto respectively.
Madara and Sasuke both dreamed of ruling the world and getting stronger than their counterparts. Hashirama and Naruto wished to stop them, just like Ashura wished to stop his brother.
As reincarnations of Indra, Madara, and Sasuke are older than Hashirama and Naruto. The reincarnations are the basic concepts of yin and yang and despite their rivalry or hatred, are drawn towards each other.
Since they are the symbol of yin and yang, it was their combined chakra that could seal Ōtsutsuki Kaguya. These are the two reincarnations of Indra and Ashura.