Another plot could involve time - traveling. Young Harry goes back in time, perhaps with the help of Hermione's time - turner or some other time - traveling device. He travels to a time when Voldemort was still vulnerable, before he became so powerful. Harry uses his knowledge of future events and his own magical abilities to defeat Voldemort in the past, thus changing the entire future and saving many lives.
In some fanfictions, young Harry might kill Voldemort by accident. For example, he could be exploring an old, forgotten chamber in Hogwarts and stumble upon a powerful magical artifact. When he touches it, it releases a burst of magic that targets Voldemort's main soul fragment, wherever he is. This causes Voldemort to perish instantly, leaving Harry to deal with the aftermath and the shock of what he has unknowingly done.
One popular 'Harry kills Voldemort' fanfic might be the one where Harry uses a unique spell combination that he discovers in an ancient magic book hidden in Hogwarts. This spell gives him an edge over Voldemort's dark magic.
One interesting plot could be how Harry and Voldemort initially react to the betrothal. Maybe Harry is completely shocked and disgusted at first, while Voldemort sees it as a way to further control the wizarding world through Harry. Another plot point might be how the wizarding community reacts. Some might be horrified, thinking it's a dark and twisted union, while others might see it as a potential way to end the long - standing conflict between good and evil.
Another plot could be the development of the relationship between Harry and Voldemort. At first, they would be extremely hostile towards each other. But as time passes, they might start to understand each other in unexpected ways. For example, Harry could teach Voldemort about love and friendship, concepts that Voldemort has long discarded, which could potentially change Voldemort's dark path.
One interesting plot could be that they are mates due to a powerful ancient magic that was long forgotten. This magic forces them to understand each other's pasts and they start to question their long - held enmity. For example, they might discover that they both had difficult childhoods which led them to their current paths, and this newfound understanding makes them consider a different future together.
After Harry kills Voldemort in the graveyard in the fanfiction, the magical balance might shift. With Voldemort gone, some of the dark magic that was prevalent might start to fade away. The Hogwarts School of Witchcraft and Wizardry could see a new golden age. New spells and magical theories might be explored as the fear of Voldemort no longer holds back the wizarding scholars. Harry himself might start to travel around the world to spread the news of Voldemort's defeat and also to learn more about different types of magic. His friends would also have new opportunities, like Hermione might be able to further her studies without the constant threat of Voldemort and Ron could finally relax and enjoy a more peaceful life at the Burrow.
In some of these fanfictions, the plot might involve Harry and Voldemort having a secret family connection. For example, they could be distant cousins through some convoluted wizarding family tree. This changes how they view each other and the conflict between them.
The wizarding world would likely be in a state of shock and then celebration. People would start to see Azkaban in a new light, perhaps no longer as just a place of horror but also as the site where the great evil was finally vanquished.
In some stories, their friendship could start from a time - travel accident. Harry gets sent back in time and ends up befriending a young Voldemort. He tries to influence Voldemort's path, and they form an unlikely bond. Harry might introduce Voldemort to different values and ideas that were not present in Voldemort's original upbringing, which causes a major shift in the future of the wizarding world.
Perhaps in the fanfiction, Harry gives up because he becomes disillusioned with the wizarding world. He may see all the corruption and prejudice within it and decides that Voldemort's way of ruling might not be much worse. This could lead to a story where Harry actually joins Voldemort's side, not as a slave but as an 'advisor' of sorts, trying to change Voldemort from the inside. However, this is a very dangerous and morally ambiguous path for Harry to take.
One interesting plot could be that they are distant relatives through some ancient wizarding bloodline. Maybe there was a curse placed on the family long ago that led to their enmity.