Well, perhaps in the fanfiction, their relatedness is discovered when a powerful magic spell goes awry and reveals hidden family ties. This could lead to a whole new dynamic where they have to reevaluate their relationship. It might also involve other characters having to choose sides based on this new revelation. For example, some Death Eaters might question their loyalty to Voldemort if it means going against their family's newfound connection to Harry.
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.
In some fanfictions, their relatedness could be tied to a prophecy that was misinterpreted for generations. Their connection might be the key to a greater magic that was meant to be harnessed for good, but Voldemort's thirst for power corrupted it. This could result in a journey for Harry to understand this connection and use it to defeat Voldemort in a more profound way than just by using the Killing Curse on him.
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.
One idea could be a fanfiction where Voldemort has a change of heart due to some ancient magic. Maybe he discovers a spell that shows him the true consequences of his actions and decides to work with Harry to fix the wizarding world instead of destroying it.
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.
In some Harry Potter fanfictions, there might be plots where characters use magic to create unique money - making schemes. For example, a character could use a spell to multiply rare magical items and then sell them at a profit in Diagon Alley. Another idea could be a wizard starting a business teaching other wizards about Muggle finances, which is a new concept in the wizarding world.
One interesting plot could be a magical duel between Harry Potter and one of the Cullens. Maybe they meet in a special dimension where magic from both universes co - exist. Harry uses his spells like Expelliarmus while the Cullen uses their vampire - related powers.
In fanfiction, Harry Potter and Voldemort are related through the prophecy that ties their fates together. This often leads to scenarios where Harry has a unique understanding of Voldemort, like being able to see into his mind. Fanfic writers may also play with the idea of a shared past or some sort of magical bond that was created before they even knew of each other. They are two sides of a magical coin in many fanfictions, with Harry representing the good and Voldemort the evil, but their relationship is much more nuanced than just that.
One interesting plot could be Lily's struggle with her identity. Being the daughter of Voldemort, she might constantly battle between the dark side that is in her blood and the good she has been taught. For example, she could be tempted by dark magic but resist it because of the friends she has made at Hogwarts.
One possible plot could be Harry trying to understand Voldemort's past and motives through the letters. Maybe he writes to ask about Voldemort's childhood, what led him to become so evil. Another could be Harry attempting to persuade Voldemort to change his ways, using the letters as a form of communication to reach the dark wizard's humanity. Or perhaps Harry writes to taunt Voldemort, using the fanfiction as a way to get under his skin and make him angry in a psychological battle.
One possible plot is that Harry discovers a hidden prophecy that says only by helping Voldemort can he truly save the wizarding world in the long run. So, he reluctantly starts to assist Voldemort in his conquests, all while secretly planning to turn the tables.