It could be that Voldemort is not entirely the evil being everyone thinks. There is some external force threatening both him and Harry. In order to defeat this common enemy, Harry decides to ally with Voldemort. They combine their powers, with Harry's unique connection to Voldemort through the scar playing a crucial role in their new - found cooperation.
Maybe Harry discovers some dark secret about Dumbledore or the Order of the Phoenix that makes him question his loyalties. This leads him to believe that Voldemort might have some valid points. So he allies with Voldemort to uncover more secrets and expose the so - called 'good guys'.
One possible plotline could be that Harry realizes the wizarding world has some deep - seated flaws that Voldemort also wants to change. So, they form an alliance to reform the Ministry of Magic. For example, they might work together to end the pure - blood supremacy that has long plagued the wizarding society.
A possible plotline could be that Voldemort has a change of heart. Maybe he realizes that Harry has some power or knowledge that he needs, so he decides to carry Harry away to a secret location to extract that information from him.
In some versions of this fanfic concept, Harry might surrender as part of a long - term strategy. He could be faking it to get closer to Voldemort and find a way to destroy him from the inside. He might endure a lot of hardships and mental torture while pretending to be a submissive prisoner, all the while looking for that one weak spot in Voldemort's defenses that he can exploit to end the Dark Lord once and for all.
One possible plotline could be Harry being held captive in one of Voldemort's dark lairs. Voldemort might use the Cruciatus Curse on him repeatedly to try and break his spirit or get information about the Order of the Phoenix. Harry could be isolated and tortured while his friends desperately search for him.
One possible plotline could be that Voldemort realizes that Harry is the key to some greater power or knowledge that he wants to obtain. So, instead of killing Harry, he saves him from another dark wizard or a dangerous magical creature. Maybe he sees that Harry has a connection to an ancient magic that could help him rule the wizarding world in a more complete way.
One possible plotline could be that Harry discovers some sort of ancient magic or prophecy that binds him to Voldemort in a way that is not initially understood as a mate - like relationship. As they interact more, they start to see different sides of each other. Harry might try to change Voldemort, and Voldemort might find himself having unexpected feelings for Harry. Another plotline could involve a magical accident that fuses their magic in a way that creates this bond. Then they have to navigate their new relationship while dealing with the wizarding world's reactions.
One possible plotline could be that Harry is tricked by Voldemort. Voldemort might use some powerful dark magic or false promises to make Harry believe that joining him is the right thing to do. For example, Voldemort could claim to have a way to end all the bloodshed in the wizarding world if Harry helps him.
One possible plotline could be Harry being held captive by Voldemort in a way that's like a pet. Voldemort might use Harry to show his power over the Boy Who Lived. Another could be that Harry has some sort of magic that makes Voldemort keep him as a pet instead of killing him immediately.
One possible plotline could be that Harry is under some sort of dark magic influence or curse that forces him to aid in Voldemort's resurrection. Maybe a powerful dark wizard has manipulated Harry's mind.
Another plotline might be their family life. They could be shown starting a family early, and dealing with the joys and challenges of raising children in the wizarding world. For example, teaching their kids magic at home, or dealing with the chaos of a family full of young wizards.
One possible plotline could be that Voldemort discovers Harry's abuse through his Death Eaters' spying. He decides to save Harry as he wants to turn Harry to his side and believes that by rescuing him, Harry will be more likely to join him. Another could be that Voldemort has a moment of self - reflection and realizes that the way Harry is being treated is wrong, so he steps in.