The Rikudo Kage has became the legend and was worshipped by ninja as a god. In Naruto Manga chapter 467 page 13, according to Uchiha Madara, the Rikudo Kage once saved the world from the 10-tailed beast called “Jubi.”

He sealed off the Jubi into his body and make use of the 10 tailed beast’s chakra.

He knew that the Jubi’s chakra was too great that it would break until the Jubi would be released and wreak havoc to the land. So, when he was dying, he divided the Jubi’s chakra into the 9 tailed beasts and disperse them into the land and then sealed its empty body and sent it off the sky which became the moon.

Based on the Naruto Manga chapter 467 page 12 as told by the Uchiha Madara, these secrets of the Rikudo Kage were carved in the tablets that has been passed through the Uchiha clan for generation. These tablets until now lie beneath Konoha in the Uchiha Clan’s secret meeting place. Those with the eyes power are those who can read them. Each eyes power level can read something from Sharingan, Mangekyu Sharingan to Rinnegan.

So since Uchiha Madara got all these level (Pain who was once with Uchiha Madara was a Rinnegan user), he knew all the info written on the tablets.

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