Kakashi's reaction would be complex. He is a man who has lost many people in his life. But Naruto was special. He would hold Naruto tightly, his hands trembling slightly. He might try to use some of his own chakra to keep Naruto alive a little longer, but deep down he knows it's futile. His face would show a mixture of pain, regret, and love. He would remember all the times he trained Naruto, all the lessons he taught him, and how Naruto had surpassed all expectations.
One idea could be that Rin, with her medical skills, tries to save Kakashi but fails due to some unforeseen circumstances. Maybe an enemy uses a powerful jutsu that she can't counter in time. This would be a tragic twist, as her being alive doesn't change the outcome for Kakashi.
One possible plotline could be that Kakashi is in a life - threatening situation during a battle against a powerful enemy. Naruto, seeing no other way to save him, uses a powerful and self - sacrificing jutsu that costs him his life. Another plotline might involve Naruto making a deal with some dark force to save Kakashi, but the price is his own life. Or perhaps in a mission gone wrong, Naruto takes a fatal blow meant for Kakashi.
In such a fanfiction, the emotional impact would be huge. Naruto is a central character, and his sacrifice for Kakashi would shock the Naruto universe. It would leave characters like Sasuke, Sakura, and the entire Hidden Leaf in mourning. Kakashi, who has always been a mentor to Naruto, would likely be consumed by guilt and a sense of unworthiness. The story could explore themes of self - sacrifice, loyalty, and the bonds between teacher and student on a very deep level.
I'm not sure of a specific 'naruto dies saving kakashi fanfiction' off - hand. You could try searching on fanfiction - dedicated websites like Archive of Our Own or FanFiction.net.
One possible plot could be that Naruto and Kakashi are in a fierce battle against a powerful enemy. Kakashi is about to be fatally attacked when Naruto jumps in front of him and takes the hit. As Naruto is dying, he might have some final words for Kakashi, perhaps about the importance of protecting the village and their friendship.
It could be a consequence of Naruto's own overuse of the Nine - Tails' chakra. Naruto has always been pushing his limits when it comes to using the Nine - Tails' power. If he overdid it in a crucial battle, it could have damaged his body beyond repair. Kakashi, as his former teacher and a trusted friend, would be the one to hold him as he passed away, mourning the loss of such a great hero.
A possible plot could be that Kakashi sacrifices himself to save Rin from a powerful enemy. This would be ironic as usually, Kakashi is the one protecting others. With Kakashi gone, Rin might then discover some secrets that Kakashi was keeping from her. These secrets could change her view of him and also drive the rest of the fanfiction as she tries to come to terms with his death and the new information.
Naruto would be extremely devastated. He sees Kakashi as a mentor and father figure. He might go into a period of deep depression at first, but then turn his grief into motivation to become stronger. Sakura would also be very sad and might focus more on her medical skills, vowing to save more lives in Kakashi's memory. Sasuke might have a more internal reaction, feeling guilty if Kakashi died protecting him, and it could further fuel his own goals, whatever they may be at that time.