One idea could be that James and Lily Potter go into hiding with Harry instead of being killed. They could use powerful magic to disguise themselves and Harry, and then raise him in a secret location, teaching him magic from a very young age. This would change Harry's whole personality as he would grow up with the love and guidance of his parents.
In a fanfiction where Harry's parents are alive, it could be that they were secretly protected by a powerful ancient magic. They were transported to a different magical realm. When they return, they bring with them new magical knowledge and spells. They help Harry become an even more powerful wizard. For example, they teach him how to combine different types of magic in unique ways. They also work to improve the relations between the wizarding world and other magical creatures.
One plot idea could be that Harry has to face the Boggart - his parents - in a more public setting than expected, like during a school-wide anti - dark arts demonstration. This could add an extra layer of pressure as he tries to keep his emotions in check. Another idea is that the Boggart - parents might start interacting with other students' Boggarts, creating a chaotic and emotional mess in the classroom. Maybe the Boggart - parents could also show signs of the dark magic that killed them, which would terrify Harry even more as he realizes how close he is to that danger.
Perhaps Harry is disowned because his parents believe he has been corrupted by dark magic. So he has to prove his innocence and find a way to reverse their decision. Along the way, he meets a mentor who helps him master his magic in a new and unique way, different from what he would have learned from his parents.
Well, perhaps Harry uses a time - turner that has been magically enhanced to travel far enough back. He could disguise himself and befriend his parents, subtly guiding them to safety. Or he could change the circumstances of their meeting, for example, if he makes sure that they meet in a more secure place. Also, he could try to influence the actions of the Marauders so that they are more vigilant in protecting his parents.
Maybe Harry's parents are alive but they've been working undercover for a long time against a different dark force that is allied with Voldemort. When they come back into Harry's life, they bring with them a whole new set of problems and mysteries. For example, they might have made some dangerous pacts with other magical beings in order to gain information. Harry has to deal with the consequences of these pacts while also trying to keep his family together. Another plot twist could be that they are alive but time - traveling is involved. They've been stuck in a different time period and Harry has to figure out how to bring them back to the present, all while Voldemort is still a threat.
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.
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.
In a fanfiction about Harry Potter and his parents, a great plot could be that Harry discovers a hidden diary of his mother. Through reading it, he gets to know her deepest thoughts, her fears, and her hopes. He also learns about the early days of the Order of the Phoenix through her eyes. This discovery could change his perspective on his own life and his place in the wizarding world. He might then be inspired to follow in his parents' footsteps more closely, perhaps by joining an organization that his parents were once part of.
A possible plot is that Harry, after being left by his parents, is raised by a wizard who lives in seclusion. This wizard has a very different view of magic compared to the mainstream wizarding world. Harry learns from him and as he gets older, he decides to go out into the world to seek revenge on those who he believes are responsible for his parents leaving him. Along the way, he meets new friends and foes and has to make some tough decisions about his path in life.