Board Thread:Naruto Discussions/@comment-36221354-20180717114536/@comment-34436445-20180717195128

For otsutsuki members you don't need a sharingan, you either are born with a rinnegan (normally all otsutsuki members are born with Byakugan) or awaken it by eating the chakra fruit like kaguya. For non otsutsuki members, you need to combine the chakra of asura and Indra or have hagomoro's chakra, but in the manga and anime all the non otsutsuki members have awakened rinnegan having the sharingan evolved into it. We have not seen any person without sharingan awaken a rinnegan.