There could be. Fanfiction is a vast realm where all sorts of ideas are explored. However, I'm not sure if there is a highly popular or mainstream 'naruto is kisame apprentice' fanfiction. It might be a more niche concept, but it's entirely possible that some creative writer has delved into this idea to create an interesting story about Naruto learning from Kisame, perhaps incorporating Kisame's unique fighting style and view of the ninja world into Naruto's growth.
Iruka could be an important character. He's always been like a father figure to Naruto, and now with this new revelation, he might have to help Naruto deal with it. Hinata could also be in the story, and her feelings for Naruto could be complicated by his connection to Kisame. And then there could be some original characters created just for this fanfiction, like a ninja who was a former ally of Kisame and has some information for Naruto.
Yes, there might be such fanfictions in the vast world of fan-created content. Some fans like to create unique family relationships between different characters from various anime, and this could be one of those interesting concepts.
She could start off as an enemy to Naruto's friends, but as she gets to know them better, she becomes more friendly. For example, she might initially be sent to spy on Sakura, but ends up respecting her medical skills. With Shikamaru, she could engage in strategic battles of wits. And with Choji, she might be intrigued by his unique eating habits and the power it gives him.
Kisame would probably be very angry at first. Samehada is his weapon and has been with him for a long time. He might feel betrayed and try to get Samehada back by force.
One idea could be a story where Naruto and Kisame are forced to team up during a mission that has a greater threat to the ninja world. They start off distrusting each other but gradually come to respect one another's skills.
At first, it would be full of suspicion. Naruto is a Konoha ninja and Kisame is from the Akatsuki. But as the teaching progresses, they might develop a mutual respect. Naruto would respect Kisame's power and knowledge, and Kisame might respect Naruto's determination.
Well, a plot could involve Kisame's sister being a healer. Naruto gets seriously injured in a battle and she is the only one who can save him. As she heals him, they start to share their stories and dreams. This leads to her realizing that the Akatsuki's ways might not be right. Also, she could be in a love triangle between Naruto and a member of the Akatsuki, which would add a lot of drama to the story. There could also be a plot where she discovers a prophecy that Naruto is the key to saving the ninja world, and she decides to protect him at all costs.
Well, in some fanfictions, Naruto might defeat Kisame in a battle and take the sword as a trophy. Maybe he uses his newfound Sage Mode powers or some other advanced jutsu to overpower Kisame and claim the sword.
In the fanfiction, it could be that Kisame gives Naruto Samehada as part of a deal. Maybe Naruto has to do something for Kisame in return. Naruto might struggle with the idea of making a deal with an Akatsuki member but decides it's worth it for the power of Samehada. Once he has it, he might face opposition from his friends and village elders who are suspicious of his new weapon and the way he obtained it.