Naruto fought the longest in war

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They're a two man team. Thus, when they fought together they shared the same amount of time fighting. Add the other half of Kurama that was fighting alongside Minato whilst Naruto was out of commission and Kurama's total time spent fighting during the war exceeds Naruto's. It's really simple.

yeah technically he was "fighting" the longest just not my definition of fighting thats like saying concentrating is fighting