Petunia could also be an important character. Despite their differences, she is Lily's sister. There could be a plot where Lily tries to reconcile with Petunia in her married life. Maybe Petunia finally starts to accept Lily's world a little bit more because of her new family.
Remus Lupin would be a great addition. He's another one of James' friends. He could offer them wise advice, especially when it comes to the more difficult aspects of their relationship or the challenges of living in the wizarding world. He might also help them out during full moons.
Sometimes, their friends like Sirius Black or Remus Lupin might also be important characters. They could be involved in the couple's life, perhaps helping them out in difficult situations or just being there for moral support.
Obviously, James and Lily are the main characters. But other characters could also be included. For instance, Sirius Black, as James' best friend, might be a regular presence. He could be the fun - loving, trouble - making friend who often drops by their house unannounced. Then there's Remus Lupin, who could be a more calm and wise friend offering advice to James and Lily on their married life. And of course, Petunia, Lily's sister, might be a part of the story, perhaps causing some family - related drama.
Well, a plotline might involve them facing challenges from the wizarding world. For example, there could be threats from dark wizards which they have to fight together as a married couple. Or perhaps they get involved in some sort of magical research as a team in their married life. Also, their relationship growth is a big part. They could have little arguments and then make up in the most romantic ways, like James bringing Lily her favorite flowers after a fight.
Well, a plotline might involve them dealing with outside threats to their family. Since they are in the wizarding world, there could be dark wizards targeting them. They would have to rely on their love and magic skills to protect each other and their home. Also, they could have adventures together, like exploring new magical places that are only accessible to married wizards.
Harry would often be a main character in these fanfictions. Since it's about bashing his parents, his reaction and how he copes with the new view of them is a big part of the story. Another could be Sirius Black. He was very close to James, so fanfictions might explore his feelings towards the bashing of his best friend.
Voldemort and his Death Eaters could be the main antagonists. Since they are against the wizarding world's light side, they would see Lily and James's unborn child as a threat, especially if there are prophecies surrounding the baby.
Petunia could be an important character. She might be grudgingly attending the wedding, still having mixed feelings about Lily's magical world. Her presence could add some tension as she struggles to fit in. And then there's Dumbledore. He could make an appearance and give some wise words of advice to the couple, perhaps about the future challenges they might face together.
It could be a dark wizard who wants to prevent Ginny from meeting James and Lily. Maybe this wizard has some grudge against the Potter family and knows that if Ginny meets them and learns something important, it will foil his evil plans.
Obviously, James and Lily Potter are the main characters as the title implies. Their return is the central event. Harry Potter is also a key character as their return would greatly impact his life.
The main characters are obviously James Albus and Lily Potter. They are likely to be the central focus of the fanfiction, with their adventures and experiences at Hogwarts being the main storyline.