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How did he die, and how powerful was he supposed to be i remember in the anime Shisui stated he was nothing compared to Kagami.
Naruto Wikia:
As an Uchiha, Kagami had very strong chakra. He was also one of the members that were able to awaken his clan's kekkei genkai: the Sharingan, which granted him various advantageous abilities. These included seeing the flow of chakra, the ability to easily recognise genjutsu and different forms of chakra, some predictive capabilities, as well as the ability to copy techniques that the user sees amongst other things. In the anime, his visual prowess was praised by Danzō to be crucial in saving his life many times. Shisui, Kagami's descendant and one of the most powerful Sharingan users of the Uchiha himself, openly admitted his inferiority to his ancestor as a shinobi.[2]
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