A lot of fanfictions in this category might explore different timelines. For instance, some might have them survive the initial attack and then change the course of the wizarding war. They could use their combined magical powers to turn the tide early on. So, look for stories that focus on these aspects when you search for fanfictions about them being alive.
Well, a really interesting 'James Potter alive' fanfic I've read is 'James Potter: The Resurrection'. In this story, James is brought back through a complex magical spell gone wrong. It's full of action as he has to deal with dark wizards who want to use his resurrection for their own evil plans. Then there's 'Living James Potter' where he has to hide his identity at first because the wizarding world believes he should be dead. It's a really cool concept as it shows how he tries to reconnect with his loved ones secretly.
One great fanfiction could be 'The Potter's New Life'. In this story, Lily and James Potter are alive and they have to deal with new threats that are different from Voldemort. It shows their parenting skills with Harry in a whole new way, and how they navigate the wizarding world with their new - found life.
In a fanfiction where Lily and James Potter are alive, the plot would be turned on its head. For starters, the Dursleys would never have come into the picture. Harry would have been raised in a loving magical family. This would mean he'd have access to all his magical knowledge and abilities from a young age without any suppression. Also, the war against Voldemort would have been fought very differently. Lily and James, being experienced and powerful wizards, would have led the charge. Their presence would have inspired a different kind of hope in the wizarding community. And think about Hogwarts - Harry would be going to school with his parents' support and influence, which could change how he interacts with his classmates and teachers.
In some 'James Potter alive' fanfictions, his character can be more mature. For example, if he comes back after a long time, he might have learned from his past mistakes. In the original, we saw him as a bit of a troublemaker in his youth. But in fanfics, he could be more responsible, especially if he realizes he has a second chance to be a better father to Harry or a better friend to his mates. He might also be more empathetic, having seen the consequences of his actions (or rather, his 'death') on those he left behind.
In some fanfictions, if Lily and James were alive, they would play a huge role in the fight against Voldemort. They could train Harry and other young wizards in secret. Maybe they'd form an underground resistance group using their knowledge of Hogwarts and the wizarding world to outwit Voldemort and his followers.
There are fanfictions where James and Lily alive means that they are part of a time - travel plot. Maybe they are sent back in time to before Voldemort rose to power. They then use their knowledge of the future to prevent the dark wizard from ever becoming a threat. In this kind of fanfiction, they would interact with younger versions of their friends and family, and have to be careful not to disrupt the timeline too much. This creates a really interesting and complex story.
A really interesting plot could be that James and Lily, alive, work with Dumbledore to create a new school of magic. This school would focus on teaching students how to defend against the Dark Arts in a more practical and hands - on way. Harry would be one of the first students there. They could also develop new magical artifacts that could help in the fight against evil. And the family could have adventures all over the world to find the ingredients and knowledge needed for these new creations.
One interesting plot idea could be that Lily and James, alive and well, decide to train Harry in magic from a very young age. This would make Harry an even more powerful wizard earlier on. They could also use their influence to reform the wizarding world, starting with Hogwarts. For example, they might introduce new courses that focus on both light and dark magic, teaching students how to defend against the dark arts in a more comprehensive way.
One plot idea could be that James and Lily go into hiding with Harry instead of being killed. They could raise him in a secret location, teaching him magic away from the prying eyes of Voldemort. Another could be that they fake their deaths and then work secretly to undermine Voldemort's forces. For example, they could use their knowledge of the Death Eaters to expose their plans and turn some of them against Voldemort.