Perhaps James had some hidden magical ability that he was unaware of until that moment. It could be something that was passed down through his family but had never manifested before. This ability could have protected him from Voldemort's killing curse. Or, it's possible that there was a plot by some other characters to save James. There could have been a group of wizards or witches who had been secretly working to keep James alive because they knew his importance in the fight against Voldemort. They might have used some sort of time - turning magic or a protective charm that Voldemort couldn't break through.
Well, if James Potter survived, it would completely change the backstory of Harry Potter. For one thing, Harry might have grown up with his father, which would have meant a very different childhood for him. He wouldn't be the orphan raised by the Dursleys. Also, James Potter was a talented wizard, so he could have been a major influence on Harry's magical education from a very young age. This would likely make Harry even more powerful and confident earlier on. And the fight against Voldemort would have been different too, as James would have been another powerful force against the Dark Lord right from the start.
Well, a great James Potter survived fanfiction is 'James Potter's Redemption Arc'. It could explore how his survival changes his perspective on life and death. Maybe he has to deal with the guilt of leaving his family behind in the first place. Then there's 'The Return of James Potter'. This one might show his struggles to fit back into the wizarding world he once knew, as so much has changed since his supposed death.
One common theme is family. Since they are father - son, many fanfics explore their relationship and how they bond over their shared family heritage. Another theme is legacy. They both carry the Potter name and the stories often deal with how they uphold or change the Potter legacy. Magic is also a big theme as they both are powerful wizards and the fanfics show their magical abilities in different ways.
One great fanfic could be 'A Father's Legacy'. It delves into James Potter's relationship with Harry through a series of magical adventures. Another is 'James and Harry: Unseen Bonds' which focuses on how James's spirit influences Harry's journey at Hogwarts. There's also 'The Potter Connection' that shows their relationship in an alternate universe where they can interact more directly.
There is a fanfic where James Sirius Potter discovers a hidden mystery in Hogwarts. In this story, he teams up with some new friends. The author does a wonderful job of creating a believable world and the relationships between the characters are really well - written. It's a great read if you want to explore more about this character.
I'm not aware of any such fanfic. Fanfiction often contains a wide variety of strange and inappropriate concepts, but this one seems rather extreme and goes against the nature of the original Harry Potter story in terms of the characters' relationships.
You can start by looking on fanfic websites such as Archive of Our Own (AO3). It has a large collection of fanfics related to the Harry Potter universe, including many that feature James Potter. Fanfiction.net is also a popular place to search. There are often communities dedicated to Harry Potter fanfic on these platforms where you can find reviews and recommendations.
Well, they might be quite amused. They could be proud to see how much the fans love their son Harry. They might also be a bit surprised at some of the creative interpretations that fanfic writers come up with.