Well, they might be shown putting the needs of the village above their own personal desires. For example, they could sacrifice their own time and resources to ensure the safety and prosperity of the village. Maybe they give up personal grudges or ambitions for the greater good of the community.
One plot point could be that a kage gives up a valuable opportunity for personal gain, like a chance to obtain a powerful jutsu, in order to use the resources to improve the village's defenses. Another could be that a kage steps down from power when they realize someone else can do a better job for the village, even though it means losing their status.
In the original, the Kages were seen as authority figures that Naruto was trying to gain the respect of. In this fanfiction, he's actively against them. This changes how other characters might view Naruto too. Some might side with him, thinking he has a point, while others would be loyal to the Kages and see Naruto as a troublemaker.
One possible reason could be a feeling of betrayal. Maybe the Kages made decisions that Naruto thought were against the greater good or the well - being of the ninja world. For example, if they were too focused on protecting their own villages at the expense of others.
In this fanfic, Naruto might show off his incredible strength and unique jutsus against the five kages. He could use his Rasengan in creative ways to counter their various powerful techniques.
It's hard to say. Naruto has his powerful Nine - Tails Chakra and Sage Mode. But the five kages are also very strong. However, Naruto has a habit of coming out on top in tough situations, so he might be the likely winner.
In a fanfiction where a missing - nin takes on the Kages, the story could go in many directions. The missing - nin could have a hidden agenda, like trying to steal a powerful jutsu or secret from the Kages. Maybe they were once a part of the village and had a grudge against the Kages. The Kages would represent the established order and power of the ninja world. Their fight would not only be physical but also a battle of ideologies. The missing - nin might be fighting for personal freedom or revenge, while the Kages are fighting to protect their villages and the stability of the ninja world.
Sasuke Uchiha could be a likely candidate. He had his period of being a rogue ninja. With his Sharingan powers, which allow him to copy jutsu and predict movements, and his own powerful ninjutsu like the Chidori and later the Rinnegan abilities, he would be a formidable opponent against the Kages.
It can show the power dynamics. For example, the Raikage might be more forceful in his opinions, while the Tsunade of Konoha could be more diplomatic. This contrast can create interesting interactions.
In such fanfiction, Sakura might be depicted as more alluring and perhaps more bold in her interactions with Madara. Madara could be shown as having a certain charm that draws Sakura to him.