Harry Potter would likely be one of the main characters. Since Ginny is his love interest in the original series, he would surely be affected by her marriage to Voldemort. He might be the one to try and rescue her or stop the marriage. Ron Weasley, Ginny's brother, would also be important. He would be outraged and would probably be part of any plan to oppose the union.
Well, a plot could be that Voldemort has a change of heart after falling in love with Ginny. He starts to question his dark ways and Ginny, seeing this potential for good in him, decides to marry him in the hopes of fully turning him around. But this is met with great resistance from the wizarding community who see Voldemort as irredeemable. Ginny then has to fight not only for Voldemort's redemption but also for their relationship to be accepted.
There is indeed voldemort marries harry fanfiction out there. Fanfiction writers often take creative liberties and imagine all sorts of scenarios that deviate from the traditional storylines. This particular concept might seem strange at first, but it allows for new interpretations and character developments within the fan - created stories.
One common theme could be redemption. Maybe the story shows voldemort changing through his relationship with harry. Another theme might be the power dynamics, as both are very powerful in different ways.
A frequent theme is the breaking of boundaries. In the original story, Harry and Voldemort are on opposite sides of a huge divide. Fanfictions with this plot explore what happens when those boundaries are shattered. Also, there can be a theme of discovery. Harry discovers a new side to Voldemort that no one else has seen, and this leads to their relationship. And of course, there's the theme of transformation, both for Voldemort in terms of his character and for the whole 'Harry Potter' world view as a result of their relationship.
One interesting fanfiction could be 'The Dark Union'. In this story, Voldemort's character is given a different perspective where his union with Hermione is a strategic move to change the wizarding world's power dynamics. It's a rather unique take on the pairing.
Well, in this sort of fanfiction, Ginny's motive could be a complex web of emotions. She might be under the influence of a dark spell. Or perhaps she has been misinformed about Harry's role and believes that by giving him to Voldemort, she's actually saving the wizarding world. It could also be a case of extreme jealousy, if the writer wants to explore a really twisted version of her character.
Yes, there might be some. However, it's a rather dark and unorthodox take on the Harry Potter universe. Some fanfictions like this explore extreme 'what - if' scenarios. But they often deviate greatly from the original spirit of the series.
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.
There's a fanfic called 'Ginny and Harry: A Love Unhindered'. In this story, they start dating right after the defeat of Voldemort's minions in their final year at Hogwarts. Without the threat of Voldemort, they are able to fully explore their feelings for each other. They go on adventures across the wizarding world, from the beaches of Cornwall in the wizarding UK to the magical markets in Paris, just the two of them.