One interesting plot could be a character from the original series getting a chance to redo a crucial moment in their life in this Second Life. For example, Harry might have the opportunity to save Sirius in a different way.
Maybe in this fanfiction, Harry's second chance at life allows him to prevent certain tragedies. For instance, he could figure out a way to save Sirius Black much earlier. He might have a premonition about what's going to happen and use his knowledge from his first life to change things. This would completely change the dynamic of the story as Sirius could play a more active role in Harry's life and in the fight against Voldemort.
Harry himself is of course very popular as the story revolves around his second chance. Hermione is also often a key character as she can help Harry with her knowledge and planning. Another popular character is Dumbledore. His wisdom and guidance are crucial in many fanfictions, and in the context of a second chance, he can play an even more important role in mentoring Harry.
In this type of fanfiction, a plotline could be Harry having a second chance at life and realizing the power of his choices. He might choose to focus more on his studies and become an even more powerful wizard. He could also use his knowledge from his first life to form alliances that he didn't before. For instance, he might befriend some of the Slytherins who were on the fence about Voldemort. This would give him an edge in the fight against the Dark Lord and also change the dynamics of Hogwarts.
It depends on how you look at it. Fanfiction is a place for creativity to run wild. While creating life in a Harry Potter fanfic might not be something J.K. Rowling would do in the official series, in the fan world, if it's done in a way that respects the characters and the overall tone of the story, it can be okay. For example, if it's a magical experiment gone wrong or right in a way that still ties into the magical laws of the Potterverse, it could be an exciting addition to the story.
In most cases, it is legal. Fanfiction is often considered a form of derivative work. As long as it doesn't violate J.K. Rowling's copyright in extreme ways, such as mass - producing and selling it without permission. Many fans create fanfiction as a way to explore different aspects of the Harry Potter universe, and the general reading of it for personal enjoyment is usually okay.
One lesson could be about friendship. In many Harry Potter fanfictions, just like in the original books, characters rely on their friends. They face challenges together and learn that true friends are there through thick and thin. For example, they might help each other study magic or fight against dark forces. This shows that in real life, having good friends is crucial for support and growth.
It keeps the fandom alive. When fans read new fanfictions, it reignites their love for the series. They get excited about new ideas and interpretations of the story.