In a world populated by soul-stealing aliens, supernaturally powered ninjas, and biologically engineered androids, a common and ongoing debate among Naruto fans is who is the most powerful ninja. While there's a good argument for more than a few characters, there is one event, an attack, that single-handedly, and persuasively reveals who's the strongest ninja ever.
Born in a time of war, just a few generations after the arrival on Earth of his family's matriarch Naruto's big villain Kaguya Otsutsuki, Madara Uchiha was blessed with all the abilities to be a great ninja. His great grandfather Indra was even the creator of ninjutsu. Being that he and his family were in a constant state of stress, he had plenty of opportunities to use and develop his ninja skills. Whereas other of his clan were less blessed with the powers ed down from Kaguya and her son Hagoromo, from an early age Madara showed exceptional Jutsu skill. Accordingly, before long he took leadership of the Uchiha clan ushering them through war and eventual peace with their lifelong enemies the Senju Clan, who had descended from his grandfather's brother Asura. One of the reasons why Madara was so powerful was because he had access to both Sharingan and the all-powerful Rinnegan.
By all appearances, Madara's powers with Sharingan and Rinnegan were made devastatingly clear in Naruto Chapter #562. Thereafter hearing that Madara had returned after being thought dead for decades, the various ninja communities banded together to eliminate the ancient ninja as a result of the war he waged on them many years ago. Despite being confronted by thousands of troops, Madara did not even flinch. Instead, using the combined power of the Sharingan, elements of Rinnegan he had from Hashiramu's body that he'd bitten off during their final battle, and the unlimited Chakra that he could access from being resurrected, Madara pulled a meteorite from outer space and just dropped it on his adversaries.
While the two Kage were initially able to stop the meteorite from continuing its fall, Madara then pulls another meteorite from the atmosphere and crashes it into the first. Buckling under the pressure of both, the Kages' resistance fails, and the two meteorites lay waste to hundreds of shinobi while sending a shockwave across the land. It's a devastating attack by Madara against numerous experienced ninja warriors. It also proves that with the combination of special circumstances present in Madara at the time he was the most powerful ninja in the Naruto world. Not even the combined forces of the Kage were unable to stop him.
While the debate over Naruto's most powerful ninja will probably continue for some time, this single event should leave little doubt that Madara has more than earned that title. If Madara Uchiha wasn't tripped up by his great-great-grandmother Kaguya's return, it's likely Naruto would be living in a Madara-run world.
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