Board Thread:Versus Debates/@comment-33229263-20171019104931/@comment-6769189-20171019115248

The Rinne Sharingan is weird. It might be an entirely different eye since it always manifested asa 3rd eye, seperate from whatever eyes the user had.

It also might be a 10 Tail/Kaguya exclusive eye, since all its users had the Juubi absorbed.

It might also be a merged Rinnegan/Sharingan. Since Hagoromo didnt have a 3rd eye at birth, he couldnt have the power of both eyes and the stronger eye(Rinnegan) took over. When Ashura and Indra were born, neither of them got 6 Paths chakra and the chakra they did get only had certain properties of Hagoromos. Without Hagoromo's 6 Paths chakra the Rinnegan fell dormant and the Sharingan manifested.

The reason i specify Hagoromo's 6 Paths chakra is because Obito recieved 6 Paths Chakra and the juubi (though it was incomplete and unmastered) his eyes didnt change into the Rinnegan. Any character with a Rinnegan got it from recreating Hagoromo's chakra. Recreating Hamuras 6 Paths chakra grants the Tenseigan.

Indra didnt literally get the same eyes, just as Ashura didnt get the horns and other weird facial features Hagoromo had despite recieving his body.

Tl;dr: Uchiha eyes contain the potential for Rinnegan, but it is only activated through Hagormo's chakra.