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.
Another possible plot is that Harry uses his second chance to study magic in a different way. Instead of just following the curriculum at Hogwarts, he delves deeper into the ancient and lost magics. He might find a way to combine different spells or magic forms that were thought to be incompatible. This could lead to him having unique powers that give him an edge against Voldemort and his Death Eaters, and also change the way the wizarding world views magic.
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.
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.
There are 'Second Chance' fanfictions where Harry has a second go at his fifth year at Hogwarts. In this scenario, he is more prepared to deal with Umbridge. He might also use his second chance to better train Dumbledore's Army from the start, making them a more effective force against the Dark Arts. Some fanfictions even have him getting a second chance to change the final battle, making it less costly in terms of lives lost.
Well, perhaps one interesting plot point could be the character getting a chance to redo a crucial event in the wizarding world. For example, if it was a character like Harry, he might get to relive the night his parents died and try to change the outcome. Another could be a different character being given a second chance to make amends for past wrongs, like Draco Malfoy getting a chance to befriend Harry and the Gryffindors instead of being their rival.
In some 'a second chance at love fanfiction', a plot could be that there was a big misunderstanding in the past that led to their break - up. Years later, through a series of coincidences, they discover the truth. This new - found knowledge makes them re - evaluate their past and consider giving their love another try. For instance, if one thought the other was unfaithful because of a false rumor, but later realizes it was all a lie.
One interesting plot could be Naruto getting a second chance to prevent the death of a beloved character, like Jiraiya. He could use his knowledge from the first time around to change the course of events and save his mentor, which would then have a huge impact on the story's development.
Maybe in this fanfiction, Harry is given a second chance to save Sirius. He could figure out a way to reach Sirius before he goes to the Ministry of Magic. He might use some new spells or magical items he discovers in his second chance to break through the Ministry's defenses and rescue Sirius in time.
One idea could be that a character who made a big mistake in the original story gets a second chance to fix it. For example, Peter Pettigrew could be given a second chance to not betray the Potters. Another plot could be a student who failed a crucial exam getting a redo and changing their academic fate. Maybe Neville could have a second chance to stand up to the bullies earlier in his Hogwarts years.
One interesting plot idea could be that a character who made a major mistake in the original story gets a second chance to redo a crucial event and changes the course of the wizarding world. For example, if Peter Pettigrew had a second chance, he might not have betrayed James and Lily, which would have a huge impact on Harry's life and the fight against Voldemort.
One interesting plotline could be characters from the two universes meeting by chance. For example, Frodo and Harry Potter might cross paths in a magical forest that exists between their two worlds. This could lead to them sharing their experiences and learning from each other's struggles against evil.