One possible plot could be that Harry discovers a prophecy that in order to truly end the dark magic in the wizarding world, he has to get close to Voldemort by becoming his assassin. So he pretends to be on Voldemort's side, all the while planning his demise.
There might be. The idea of Harry being Voldemort's assassin is quite an interesting and unorthodox take on the original story. Fanfiction writers love to explore these kinds of unique ideas. However, it may not be a common theme, but with the huge number of fanfictions out there, it's possible to find one. You could also check some Harry Potter - themed fanfiction communities or forums where people might recommend such works.
One possible plot could be that Harry discovers a prophecy that ties his and Voldemort's fates together in a more intimate way than just being enemies. This leads him to seek out Voldemort to understand it better. As they interact, they find themselves attracted to each other. Voldemort, who has always been alone in his pursuit of power, starts to question his motives, and Harry tries to convince him to turn away from the dark path. The plot would be filled with internal and external conflicts as they navigate their relationship and the consequences it has on the wizarding world.
Perhaps the plot could start with Voldemort finding a way to capture Harry and turn him into a cat for his own amusement. Harry, as a cat, has to navigate the dark and dangerous world of Voldemort's lair. He could make unexpected alliances with some of Voldemort's minions who might have a change of heart. Meanwhile, his friends are desperately searching for him, not realizing he's been turned into a cat. As the story progresses, Harry could find a way to reverse the spell and use his new - found knowledge of Voldemort's secrets to finally defeat him.
Well, it depends on the specific fanfiction. Some fanfiction authors might choose to take this rather radical approach and make Harry Potter into Voldemort's assassin for various reasons. Maybe they want to explore a darker side of Harry's character, or perhaps they are trying to rewrite the whole story from a completely different perspective. For example, they could be imagining a scenario where Harry has been corrupted by some dark magic and turns against Voldemort in a very unexpected and unorthodox way.
One possible plot could be that they are forced to be partners to save the wizarding world from an even greater threat. Maybe an ancient evil that neither of them can face alone. So, they have to put aside their differences and work together, which would be a huge change from their usual enmity.
In a 'harry joins voldemort fanfiction', perhaps Harry discovers a dark secret about the wizarding world that makes him think Voldemort was right all along. It could be something about the Ministry of Magic being corrupt and Voldemort's way of ruling, although extreme, is the only solution. So he joins Voldemort to 'fix' the wizarding world.
One possible plot could be that Harry is magically transformed into a panther by Voldemort as a form of punishment or control. Harry, in his panther form, has to find a way to break the spell while also trying to gather information about Voldemort's plans. He might use his new form's abilities, like stealth and speed, to his advantage.
Well, it could be that Voldemort has a strange fascination with wolves and decides to turn Harry into one as part of his plan to create a super - being under his command. Harry, in his wolf form, retains his own consciousness and memories. He has to endure the instincts of the wolf while also plotting against Voldemort. He might use the wolf's enhanced senses to gather information about Voldemort's lair and his plans, all while pretending to be under Voldemort's control.
In a fanfiction with this premise, the plot might involve Harry being raised by the Dursleys as normal, but then strange things start to happen that make him question his origins. Maybe he has some unexpected magical abilities that are a result of his unique parentage. He could then start to search for the truth, which leads him to uncover secrets about Severus and Voldemort's past relationship and how he came to be. Along the way, he would have to deal with the consequences of this new knowledge, both in terms of his own self - image and how the wizarding world views him.
One possible plot could be that the daughter is completely different from Voldemort. She doesn't share his dark ambitions and is instead a kind - hearted person. Harry discovers this side of her and gradually falls in love. They then have to face the prejudice of the wizarding world who can't believe Harry would love the daughter of their greatest enemy.