Board Thread:Naruto Discussions/@comment-142748-20150403221647/@comment-24347194-20150403231449

Maybe to awaken the Complete Body Susano'o, the user simply needs to have their Mangekyo Sharingan exponentially strengthened; both the EMS and Six Paths Chakra empowered their user's Mangekyo Sharingan greatly. This also may explain why users of the Susano'o can use the technique with the Rinnegan, since it is an evolved and stronger form of the Sharingan.