The plot could involve Naruto being shunned by the Hidden Leaf Village for some reason and Kisame, seeing an opportunity, takes him in. Kisame might see Naruto as a tool at first, but as time passes, he develops a sort of father - son bond with him. Naruto would then have to deal with the fact that he's now associated with the Akatsuki, which would put him at odds with his former friends. He could use this new position to try and change the Akatsuki from within, with Kisame's begrudging support.
In this fanfiction, perhaps Naruto is on a quest to learn more about Kisame. He could meet people who knew Kisame and through them, uncover secrets about his supposed father. This could lead to him having to make difficult decisions, such as whether to follow in Kisame's footsteps in some aspects or completely break away and forge his own path as a ninja.
Well, it could be that Naruto's relationship with the other Konoha ninjas changes drastically. They might see him as an outcast because of his association with Kisame. On the other hand, Naruto might try to bridge the gap between Konoha and the Akatsuki due to his upbringing by Kisame. This would create a whole new set of conflicts and alliances within the Naruto universe.
The plot could involve Naruto using Samehada to gain an understanding of the Akatsuki's motives. Since Samehada has a connection to the Akatsuki through Kisame, it might hold some secrets. Naruto could use it to track down other Akatsuki members or find out more about their plans.
Naruto would likely become more reserved. Since Kisame is not as expressive as some of Naruto's friends in the Leaf Village, Naruto would pick up on that. His fighting style would also change. He'd probably be more stealthy and calculating, learning from Kisame's experience. For example, instead of his usual head - on attacks, he'd start to use more misdirection and ambush tactics.
One possible main plot could be the adjustment period for Naruto. He's used to being alone, and suddenly having Kisame and Itachi as his adoptive fathers would be a huge change. They'd have to teach him different skills. Itachi might focus on Naruto's chakra control and strategic thinking, while Kisame could train him in more physical combat aspects. There could also be a sub - plot about how the village reacts to Naruto being adopted by two former enemies.
In a 'naruto adopted by hiruzen fanfiction', the plot could involve Naruto having a closer bond with the older generation of shinobi. Hiruzen would surely introduce Naruto to his trusted comrades. Naruto could learn unique jutsu from them. Also, his growth as a ninja would be different. Instead of seeking attention through pranks, he might focus more on living up to Hiruzen's name. His relationship with Sasuke could also be affected. Maybe they would become rivals in a more positive way, with Naruto having a stronger sense of family and purpose because of Hiruzen's influence.
Well, perhaps in this 'naruto adopted by grayfia fanfiction', Naruto's own world is in chaos and he gets lost in a portal that leads him to Grayfia's realm. Grayfia sees Naruto's potential and loneliness. She adopts him and starts to train him in the ways of her world. Naruto could struggle at first, but his determination from his ninja training helps him. He might get involved in local disputes or power struggles in Grayfia's world and use his unique abilities to make a difference.
If Naruto was adopted by Tsunade in fanfiction, he would probably be exposed to a different set of values. Tsunade is a strong - willed and sometimes reckless woman. Naruto could pick up on her fearless attitude towards battle and also her more practical approach to leadership. Also, their relationship might change the power dynamics in the village a bit, as Naruto would be directly under Tsunade's wing.
Well, one possible plot could be that Naruto, being adopted by Yugito, would learn a lot about the Nibi (Two - Tails) from her. Yugito could train Naruto in unique ways that combine the skills of Konoha and her own special techniques related to the tailed beast. Naruto might also gain a new family - like bond with Yugito, which could help him deal with his own feelings of loneliness from his past.
Well, one possible plot could be that Naruto is somehow transported to the Star Wars universe. The Jedi sense his strong force potential within him, which is similar to his chakra in his own world. They decide to adopt him and train him in the ways of the Jedi. He might struggle at first with the different concepts and rules, but his determination from his ninja training helps him adapt quickly.