Konan's statement was mere speculation, she has no knowledge of the rinnengan's techniques nor their rudiments. Nagato himself knew nothing beyond
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She bears no credibility hence, Obito's statement that he regurgitated from Madara himself that the Requirement of Rinne Tensei are the users soul over-rules konan's assumption. Obtio's original intention was for nagato to sacrifice himself reviving Madara. He couldn't complete his "fantasy world" without Madara himself simply because
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, which is a perfect counter in aiding his personal intentions. Without Nagato as a substitute, obito would have to revive Madara himself, taking his own life. kabuto wielding Madara as an Edo could've gained control of the war hence he was timid...and its
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that obito was unaware of Madara's full potential which further saturated his fear.