[Reiashi Gure]

I know it likely won't happen but just in case it ever is allowed I have an idea for a system for it that I had on an old site.

Rinnegan System part 1: How to obtain it.
Method one: be an Uchiha and obtain a physical amount of senju cells (like a piece of skin about the length and width of the top of one's forearm. or enough blood to fill a coffee mug.)
Method two: be a Senju and gain a Uchiha's eye(s)
Method three: be a mix of senju and Uchiha and get a small amount of the dormant blood's DNA. (Hiruko Uchiha is a Senju Uchiha hybrid, she'd just need a small amount of Senju DNA to get it. Kazuma is Hiruko's counter part and needs merely some Uchiha Blood to do so. The DNA they obtain for all above methods must of course from a member who actually HAS the kekkai genkai)
Method four: gain them from someone who already has them. Rather than physically removing them, one can send the chakra linked to their Rinnegan and sends it to the other, giving them it without having to loose one's eyes. ONLY upon death can their chakra leak back to the person who gave it to them.


Part two: technique! [wip]

Of course, just because you HAVE the eyes doesn't mean you know how to use them. However, you remember rumors of a strange tablet that only those with a ripple patterned dojutsu can read. After reading this one may be able to learn any of the following Rinnegan Techs:

naruto.wikia.com/wiki/Six_Paths_Technique
naruto.wikia.com/wiki/Animal_Path
naruto.wikia.com/wiki/Asura_Path
naruto.wikia.com/wiki/Chibaku_Tensei
naruto.wikia.com/wiki/Human_Path
naruto.wikia.com/wiki/Naraka_Path
naruto.wikia.com/wiki/Outer_Path
naruto.wikia.com/wiki/Preta_Path
naruto.wikia.com/wiki/Six_Paths_of_Pain