We got nothing on the back story of Indra and Ashura, Narutowiki gave us more on Ashura, like his nature types and jutsus. On Indra it only states one thing under jutsu and that's susanoo, and for nature types it only mentions Yin release...
The manga gives us nothing on the story, only little pieces like, black zetsu tempted Indra, but we don't know with what, in the databook it said Indra created ninjutsu, so I don't know what they used to fight before then considering ninshuu was created for peace.
We also don't know if Hagoromo gave people who weren't born with chakra any type of chakra in order to connect people, but if Indra created ninjutsu to start wars, and others used it for that, did they get chakra somewhere?
Because at the time only Kaguya, Hagoromo, Hamura, Indra and Ashura have chakra, and they got it because of Kaguya eating the fruit and passing it down through genetics to her offspring, and they pass it down the same way through thier offspring.
Still not sure where she comes from originally, seen as Kishi left that out, with Hagoromo saying that where Kaguya came from is not important.
Did Hagoromo hand out chakra in teachings trying to connect everyone? Or only to Ashura as a power up when he became successor?