Board Thread:Theories and Speculation/@comment-35023081-20190918151946/@comment-33286580-20190918170817

the Rinnegan can only awaken when Indra and Ashura's chakra are combined, or someone like Sasuke recieves it directly from Rikudo Sennin.

Hashirama being Ashura reincarnated would all but need some sort mean to permenantly acquire Madara or any other Indra reincarnates Chakra and he would be able to awaken the Rinnegan.

it is what Madara did. he got a piece of Hashirama and transplanted it in his body thus acquiring permenant access to Hashirama, as in Ashura's, CHakra.

And no... not other Uchiha or Senju DNA or Chakra will work. it has to be reincarnates of Ashura and Indra.

and also no, it does not have to be the Sharingan.

Rinnegan is a stand alone jutsu and not an evolution of Sharigan. the Hagoroma one was anime filler and not manga cannon.