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.
In 'Harry Potter second chance fanfic', a fascinating concept is a second chance for the House rivalries. Maybe Gryffindors and Slytherins getting a chance to understand each other better. For instance, Draco Malfoy could be given a second chance to not be so influenced by his family's dark views. This could lead to him becoming friends with Harry and his friends. Also, characters like Luna Lovegood could have a second chance to share her unique knowledge more widely, which might help in solving some of the mysteries in the wizarding world much sooner.
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.
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.
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.
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 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.
A great Naruto Hinata second chance fanfiction is the one where the village elders encourage Naruto to consider Hinata as a potential partner for political reasons at first. But as they spend time together, they rediscover each other and fall in love all over again. This one has a lot of political intrigue in the background while focusing on their relationship development.
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.
One interesting Harry Potter 1945 fanfiction could be about the early days of Hogwarts and how the magical world was different back then. Maybe it focuses on the founding of certain magical traditions that we see in the main series but are not fully explored. For example, it could detail how the houses were originally established and what the selection criteria were like in 1945.