Sakura would probably be very shocked at first. She might be worried about Naruto's well - being and also a bit fearful of the combined entity. Kakashi, on the other hand, would be more understanding. Given his connection to both Naruto and Obito, he would try to communicate with the merged form to figure out what happened. Sasuke would be initially suspicious, thinking it could be some new threat. But after seeing that Naruto's essence is still there, he might be more accepting and see it as a new power to use against their common enemies.
Minato might also be a prominent character. As their teacher, he can influence the way Obito and Kakashi interact. In some fan fictions, he could be the one to help them resolve their differences or provide some crucial information about their past that changes their current situation.
Obito's influence would likely make Naruto more aware of the darker side of the ninja world. Naruto is usually very optimistic, but with Obito's guidance, he would see the hardships and betrayals that can happen. For example, Naruto might become more cautious in his trust of others.
One possible fanfiction could be about Naruto and Obito teaming up to face a new, powerful enemy. They could combine their unique skills, like Naruto's Rasengan and Obito's Kamui. Their relationship could start off rocky due to their past differences but gradually turn into a strong bond as they fight side by side.
Some fanfictions might explore the emotional aspect of their fight. For example, how their past friendship affects the battle. Maybe Kakashi hesitates to strike a fatal blow because of their shared history.
Some fans would be really shocked and sad. Kakashi is a very popular character, and his death at the hands of Obito would be a huge blow to many. They might feel angry towards the author for creating such a tragic scenario.
He'd probably be very intrigued. Percy has a penchant for adventure and new things, and this fanfiction would be something completely different from what he's used to.
Besides Obito, Sasuke could be a main character in this fanfiction. Sasuke, with his own journey of redemption and his understanding of power and the ninja world, could have an interesting dynamic with the reincarnated Obito. Also, Sakura might play a role. She could be the one who tries to heal the reincarnated Obito, both physically if he is injured during his new adventures and emotionally from the traumas of his past life.
One great fanfiction about Obito being revealed in Naruto could be one where his true motives are slowly uncovered not just by Kakashi, but by the entire ninja world. It could start with small hints that the Akatsuki's actions are somehow related to Obito's past and his broken dreams. As the story unfolds, characters like Naruto start to put the pieces together, realizing that Obito is not just a random enemy but a product of the shinobi world's failures. This type of fanfiction often delves deep into Obito's psyche, exploring his love for Rin and how it was twisted into hatred after her death.