Board Thread:Naruto Discussions/@comment-1512913-20170417105433/@comment-25122992-20170417113154

Well, not sure about Izuna retaining an EMS part of his own eyes after their possession by Madara, but as for me, Izuna wouldn't be able to handle these eyes in Rinnegan form as masterfully as Madara if they were to return to him. My point is that technically it was Madara who developed these eyes into Rinnegan, not Izuna, thus he is the original owner of the newly-awakened Rinnegan, not Izuna. This developement wouldn't even be possible without Madara taking part in it since he's the inheritor of Indra's chakra, one of the necessary components for the Rinnegan to emerge. As such, I mean that Izuna's eyes with Madara as an owner went far beyond the level they reached when they stayed by Izuna, and because this power wouldn't be natural for Izuna himself, he would never achieve the same skill as Madara in wielding these Rinnegan-turned eyes, though he'd still be able to use them like Nagato or Obito did.

In general, I can summarise my opinion like that: the original owner of a certain doujutsu isn't necessary the one whom the eyes themselves naturally belong to, but the one who awakened these eyes into the said doujutsu (i.e. Madara is the original owner of the EMS awakened from Izuna's eyes and the original owner of the Rinnegan awakened from Indra's + Asura's chakra mix, or Sasuke is..., or Toneri is the original owner of the Tenseigan awakened through Hanabi's eyes etc), regardless if he used some external means like eyes/DNA transplantation or not.