Well, a possible plot twist could be that Snape has a hidden identity or past that is only revealed after he and Harry get married. Maybe he is related to an ancient wizarding family that has a connection to Harry's own family history. Also, the way Ginny died could be a misdirection. It could turn out that she faked her death to escape some greater danger, and when she returns, she finds Harry married to Snape, creating a huge love triangle and a whole new set of complications in the fanfiction.
Some characters might be completely shocked. For example, Ron, who was Harry's best friend, would probably be very confused and perhaps even a bit angry at first. Hermione, on the other hand, might try to be more understanding and look at the situation from a logical perspective. The wizarding community as a whole would likely be divided. Those who were close to Ginny would feel a sense of betrayal, while others might be more open - minded and see it as an unusual but possible development in this fictional scenario.
One plot twist could be that Snape is actually mentoring Harry on behalf of Dumbledore from beyond the grave. Maybe Dumbledore had some secret plan that he didn't get to fully execute, and Snape is now following through with it. Another could be that Snape discovers a new magical ability in Harry that no one else knew about.
One possible plot could be that after the war, both Harry and Snape realize they have a deeper understanding of each other. They start to communicate more, initially about the events that transpired. As they talk, they find common ground in their experiences of loss and loneliness. Slowly, feelings develop, and they decide to give a relationship a try. Eventually, they get married in a small, private ceremony attended only by their closest friends who have come to accept their relationship.
One plot twist could be that Harry is actually protecting Ginny and the real father. He might know some dark secret about the father that would put them in danger if it were known, so he pretends to be in the dark about the situation.
A really interesting plot twist could be that Snape was under a spell all along that made him seem so cold and distant, and Hermione discovers it. This changes the whole dynamic between them. Another twist could be that Hermione is actually related to someone from Snape's past in a way that they never expected, which brings them closer.
A great plot twist could be that Harry and Luna's marriage is part of a prophecy that no one knew about. As they are in hiding, they start to have strange dreams that lead them to uncover this prophecy. It turns out that their union is crucial for the balance of the wizarding world. But there are those who want to stop it, so they have to fight against not only the threat of discovery but also those who oppose their prophesied union.
Well, a plot twist might be related to their families. What if Harry's fame starts to cause problems in their new neighborhood? Some people might be too curious or intrusive. Also, Ginny could get an unexpected job offer in a far - off place, and they have to decide whether to stay in their new home or move again. And it could be that there's a magical creature living in their attic that they didn't know about at first, and it causes chaos in their new living situation.
One possible plot twist could be that while exploring the Department of Mysteries, Harry and Ginny discover a hidden prophecy related not just to Harry but also to Ginny. This prophecy might reveal that Ginny has a crucial role to play in the final battle against Voldemort that no one had anticipated before.
The plot could take a really interesting turn when it comes to Voldemort. Since Snape is raising Harry, he might train Harry in a way that Voldemort doesn't expect. Maybe Harry would be more of a spy in the dark side's camp. Snape could also use his position to mislead Voldemort about Harry's true abilities and intentions. This would create a whole new set of challenges and power dynamics in the fight against the Dark Lord. Harry's loyalties would be constantly tested, and his relationship with Snape would be even more crucial to the story.
One possible plot twist could be that Snape saves Harry in a very public way, which shocks everyone in Hogwarts. Maybe Umbridge was about to use an illegal and extremely harmful spell on Harry during a public 'interrogation' session, and Snape steps in at the last moment, revealing some long - hidden information about Umbridge's true nature that even Dumbledore wasn't fully aware of.