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.
They might choose to simply ignore the outside world's reaction at first. After all, they are in hiding for a reason. But as time goes on, they could start to send out messages through trusted friends to let people know that they are happy and their marriage is a positive thing.
One plot twist could be that they have to keep their relationship a secret at first due to the wizarding society's conservative views. Another could be that Voldemort uses their relationship as a way to divide the wizarding community. For example, he could spread false rumors about their union being against wizarding laws.
One possible plot twist could be that Blaise Zabini's family secrets come to light during their relationship. Maybe there are dark family alliances or hidden magical artifacts in his family's history that impact their marriage. For example, an old family curse that starts to affect Harry.
A possible plot could be that after the defeat of Voldemort, Harry and Luna start to get closer while helping to rebuild Hogwarts. They discover a hidden part of the castle together and that shared adventure leads to their relationship blossoming and eventually getting married.
Well, perhaps a plot twist could be that an old enemy resurfaces but this time they target Hinata to get to Naruto. This forces Naruto to not only protect his new wife but also figure out why this enemy is after her specifically. It could also add a layer of drama if Hinata decides to take matters into her own hands and train secretly to be able to defend herself and Naruto better. Or, there could be a political plot twist where their marriage causes unrest in the ninja world because of Hinata's family status and Naruto's position as a hero, leading to them having to fight against those who oppose their union.
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.
A plot twist might be that the goblins turn against Harry midway through his visit. They could be influenced by a dark wizard who has a grudge against Harry. This would completely change the course of his visit and force him to find a new way to achieve his goals in Gringotts. Another possibility is that the vault contains a magical item that has a mind of its own and tries to possess Harry when he touches it.
Perhaps Daphene is a foreign witch who comes to Hogwarts for some special exchange program. Harry is assigned to show her around, and they start to bond over their shared love for magic and adventure. As time passes, they realize their feelings for each other are deeper than friendship. Their marriage could then be a way to bring together two different magical cultures, with the fanfic exploring how they deal with the differences and similarities.
One possible plot twist could be that adult Izuku's knowledge of future events gets distorted as he travels to the past. Maybe he remembers things wrongly and ends up causing more chaos instead of preventing disasters. For example, he might think a certain villain will attack at a specific time, but in the past, the villain's plans were different. Another plot twist could be his relationships with the past versions of his friends. They might not trust him immediately, thinking he's some sort of impostor or has ulterior motives. This could lead to some interesting character dynamics as he tries to prove himself and gain their trust.
Well, perhaps Harry could discover the unique flora and fauna on Pandora. He might meet the Na'vi and learn their ways, like how to ride a banshee. And he could use his magic in unexpected ways in Pandora's environment.