Board Thread:Theories and Speculation/@comment-29769110-20161017201027/@comment-32196880-20170912123821

Thekillman wrote: Nope. It's enough to have Hagoromo's chakra, a Sharingan isn't needed. A Sharingan is defnitely required to manifest a Rinnegan. Only four people have possessed Rinnegan of their own(Hagoromo, Madara, Sasuke and Momoshinki) and all of them possessed a Sharingan. Uchiha can manifest only upto the Mangekyo Sharingan and only Otsutsuki can awaken a Rinnegan(if they already possess a Sharingan). That is why an Uchiha requires Senju chakra(although Otsutsuki chakra can boost chakra reserves by a greater extent than Senju chakra) to manifest a Rinnegan. If just Hagoromo's chakra is enough, then why didn't Ashura Otsutsuki or Naruto manifest one? Ashura specifically said that he doesn't possess a Sharingan, otherwise he would have awakened the Rinnegan when Hagoromo gave Ashura his chakra.

Hence, manifesting a Rinnegan is much more complicated; just having Hagoromo's chakra isn't enough.