One common scenario could be Percy revealing his true identity to save his friends. For example, in some fanfictions, his friends might be in danger because of a misunderstanding about him. So, he reveals himself as a powerful or special being to clear the air and protect them.
In some fanfictions, when Woody reveals himself to Andy, it could be a very emotional reunion. Maybe Woody has been lost or on an adventure far away, and his return brings back all the great memories they had together. Andy might be overjoyed to see his old friend again and they could start a new adventure right in their own backyard.
In fanfiction, when Harry Potter reveals himself, it could be a moment of great drama. Maybe he reveals his true identity to save his friends from a dangerous enemy. For example, if they are being tricked by a Death Eater in disguise, Harry might step forward and expose himself to stop the harm.
The Joker might be furious. His identity has been his biggest secret and Batman taking that away is like stripping him of his power. He could go on a wild rampage, more so than usual, targeting Batman directly and also anyone who he thinks might have had a part in the revelation.
The father's reaction varies. In a particular fanfiction I read, the father was first in disbelief. He couldn't believe that the young man in front of him was his son Merlin. Then, as Merlin showed some signs or told some stories that only his son would know, the father became overjoyed. He started to tell Merlin about their family history that Merlin didn't know before, which was a very emotional and bonding moment between them.
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.
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.
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.
As a fan of web novels, I don't have the latest information about iPartment 4. However, according to my knowledge, iPartment 4 is a TV series, and the plot has not been publicly announced yet. If I have more information, I will try my best to answer your questions.
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.