Nagato received the Rinnegan because Madara Uchiha transplanted his own Rinnegan eyes into Nagato when he was a baby. Madara chose Nagato specifically because Nagato was a member of the Uzumaki clan, which shares strong life force and chakra traits with the Senju clan. This made Nagato's body suitable to handle the immense power of the Rinnegan, even though Nagato himself was neither Uchiha nor Senju by blood. Madara implanted the Rinnegan into Nagato as part of his plan to have a future vessel capable of using the Rinnegan's powers and eventually reviving Madara through the Rinne Tensei technique. Nagato grew up in the Hidden Rain Village (Amegakure), away from the eyes of Konoha, which made him an ideal candidate for Madara's scheme
. In summary:
- Madara awakened the Rinnegan late in life by combining Uchiha and Senju powers.
- Knowing he wouldn't live long, Madara transplanted his Rinnegan into Nagato, an Uzumaki descendant.
- Nagato's Uzumaki lineage gave him the vitality to wield the Rinnegan.
- This was done secretly when Nagato was a baby in Amegakure.
- Nagato eventually used the Rinnegan as the leader of Akatsuki and nearly destroyed Konoha.
- After Nagato's death, Obito took the Rinnegan eyes for Madara's revival
Thus, Nagato's Rinnegan was not naturally awakened but implanted by Madara as part of a long-term plan.
