Board Thread:Naruto Discussions/@comment-34436445-20181208160828/@comment-1751565-20181208202145

Sasuke was healed using Hashi Cells by Kabuto...Probably transplanted em to heal his organs etc...and also, just before, Hashirama himself passed on his chakra and a jutsu to seal Sage Chakra to Sasuke, which is why Sasuke went after Madara, remember?

Probably because of those two things, he was able to awaken One-Eyed Rinnegan,...along with the Sage of 6 Path's boost of help, when receiving the Six Paths Shadow Style.