Re: Uchiha Tablet
As was stated earlier in this thread, and I agree with. Unlike traditional Kekkei Genkais, the Rinnenegan doesn't SOLEY require the host to have traumatic and life threatening situation. It also requires the world to be suffering from war and strife, anger and hatred, these emotions have to be very heavy in the air for an uzimaki to awaken their rinnenegan.
Kushina also said that other countries feared the uzimaki's jutsus, and so they attacked the eddy village relentlessly to wipe them out.
Perhaps the rinnenegan is one of those jutsu.
All we know from the manga, is that the Sage of six paths had rinnenegan, and Nagato Uzimaki had it.
Tobi claimed he gave rinnenegan to Nagato, but never justified or explained that statement. And while I haven't made the effort to go find the exact page of the manga yet, I'm fairly confident that durring his training with jiraya, nagato awoke another ripple in his rinnenegan, like the sharingan awakening tamoe at a time.
So if Tobi is to blame, likely it's because he put that war into motion, he put nagato in the middle of the battle field, exposed him to all that hostility in the air, coupled with the trauma of his parents death, and viola he got lucky and a rinnenegan. Or maybe he did that to several uzimaki children and only nagato woke a rinnenegan. either way I look at tobi claiming the rinnenegan, as more of a farmer claiming the apple. The farmer planted the seed, tended the soil, and allowed the tree to grow, and eventualy bear fruit. That's what he did with nagato, he planted him, put all the proper ingredients around him, and waited for him to bear fruit, of the rinnnengan.