Why do Indra and Ashura reincarnate?


The anime tells us that Madara-Hashirama and Naruto-Sasuke are the
reincarnations of Indra and Ashura.

Why did they get reincarnated? For fulfilling what purpose?




There is a lot of debate that the reincarnation cycle began because Hagoromo
knew that sometime Kaguya would be free of the Planetary Devastation seal, and
restart the Divine Tree ritual which would consume human-kind. But that is
just in terms of giving the plot a direction.

Scientifically speaking, energy can neither be created nor destroyed. All it
can do is transform. Kaguya initially attained massive amounts of
chakra/energy due to being a member of the [Otsutsuki
Clan](https://naruto.fandom.com/wiki/%C5%8Ctsutsuki_Clan), and that energy
exponentially grew larger after she consumed the Chakra Fruit. When she had
kids, which were Hagoromo and Hamura, they inherited part of her energy. After
they sealed Kaguya, the only people who wielded destructive energies were
Hagoromo and Hamura. But, Hamura left Earth to live on the moon to keep guard
on Kaguya, and the older brother Hagoromo stayed on Earth, and then had two
kids, Indra and Asura, who also inherited part of their parents energy. They
then grew up and became able-bodied adults who could use Hagoromo's power of
Ninshu, _not Ninjutsu_ , as Hagoromo said. While Indra retained and focused
the power to himself, and used it destructively, Asura, however, used it to
help people, thus forming the earliest concept of Yin and Yang. They were
beings wielding enormous power and when they died, their chakra/power were
transformed into their reincarnates, and like how opposite poles attract, so
were the reincarnates drawn towards each other.

It is also evident that Hagoromo could transcned his consciousness over time,
as he did with Naruto and Sasuke. It was just that his chakra wasn't being
transformed and remained as a silhouette over generations.

