Well, having six arms would give Naruto more options in combat. He could use multiple jutsus simultaneously. For example, he could form Rasengan in three hands while using shadow clones with the other three to distract his opponents. This would make him more unpredictable and powerful in battles.
In some Naruto fanfictions, chakra arms can be used for enhanced combat. For example, they can be extended to strike enemies from a distance. They might also be used to grapple and throw opponents with great force, similar to how Naruto sometimes uses his shadow clones for creative combat maneuvers.
Another option could be Rock Lee. He's always been about physical strength and unique fighting styles. If he were to have blade arms, it would completely change his fighting dynamic. He could incorporate his existing taijutsu skills with the new blade arm abilities, and it would be interesting to see how he trains to master this new power.
Maybe it's some kind of experimental jutsu gone wrong. Some rogue ninja or a mad scientist - type character could have been experimenting on Naruto, and as a result, he ended up with six arms.
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 a story where the character with blade arms has to protect a hidden village from a new and powerful enemy. Maybe they use their unique blade arms to fend off attacks and discover a secret about their origin in the process.
Well, in many Naruto fanfictions, the chakra arms can possess the ability to phase through objects. This allows the user to bypass defenses or reach into hidden compartments. Additionally, some fanfictions depict chakra arms with the power of energy projection. The user can shoot out powerful blasts of chakra from the arms, which can cause massive destruction. And there are also those where the chakra arms can be used to create illusions, deceiving the enemy into thinking there are more attacks or threats than there actually are.
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.
Sasuke might be in shock at first. He can't believe that Naruto is dying in his arms. He may feel a great sense of guilt, thinking that he could have done more to prevent it.
Well, in some versions of this fanfiction, it might be that Naruto uses a powerful and forbidden jutsu to defeat an overwhelming foe. This jutsu drains his life force, and Sasuke, who has just realized how much Naruto means to him, catches Naruto as he collapses. It could also be that Naruto is poisoned, and Sasuke tries his best to save him but fails in the end, and Naruto passes away in his arms.