On Naruto's side, he would probably feel guilty after realizing what he had done. This guilt could make him try to make amends, but Sakura's initial reaction of anger and hurt would still be a big obstacle in their relationship. Their interactions would be filled with tension and awkwardness.
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.
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.
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 'Naruto and Obito Fanfiction' is 'The Redemption of Obito'. It explores Obito's journey towards redemption in a really interesting way, showing how his relationship with Naruto could potentially change his fate. Another one is 'Naruto and Obito: A New Bond' which focuses on them forming an unexpected alliance and facing new threats together. There's also 'Obito's Second Chance with Naruto' that delves into Obito getting a chance to make things right with Naruto's help.
Their friendship in fanfiction could be really interesting. Maybe they start as rivals but then realize they have a common goal. For example, protecting the Hidden Leaf. They could learn from each other's jutsu. Naruto could learn about space - time ninjutsu from Obito while Obito could learn about Naruto's positive attitude towards life.
In some fanfictions, Sakura's punch might be part of a comical situation. For example, Naruto says something really stupid and Sakura just can't help but punch him. But this punch then leads to a series of adventures as Naruto tries to get back at her in a friendly way.
I recommend 'The Punch that Changed Everything'. In this fanfiction, Sakura's punch makes Naruto see the error of his ways regarding a certain mission. It's a short but impactful read.
Well, Naruto would probably be in a great deal of pain. He might double over and be unable to move for a while. It could also lead to a big argument between him and Sakura, with Naruto feeling betrayed and Sakura perhaps realizing she overreacted.
I really like 'Obito's New Path'. In this fanfiction, Obito gets a second chance in a different reality. His Sharingan abilities are explored in unique ways, like how he uses it to understand the true nature of the ninja world. The story also has great character development for Obito and other Naruto characters.