Board Thread:Theories and Speculation/@comment-26889573-20151008053113/@comment-27087341-20151017173854

The rinnesharingan is Kaguya's power born from when she assimilated the shinju power. Kaguya and Shinju's bonding created the rinnesharingan. I think spiritual power is manifested from your deepest desire. Kaguya needed a form of control over humans so with the power of the shinju she awoken the rinnesharingan. Just speculation tho.