One possible plot twist could be that the twins are actually not related by blood but are part of some mysterious experiment. This would turn their whole identity and purpose as detectives on its head.
A really interesting plot twist could be that the villains they are after are actually working for a higher power that the twins have a connection to, perhaps a long - lost relative or an organization that their family was once a part of. This would create a complex web of relationships and motives that the twins have to untangle.
The villains are also important main characters in a way. They could be other spirit detectives who have gone rogue or some sort of dark entities in human form. Their actions and motives drive the plot forward as the twins try to stop them.
One interesting plot twist could be that the forgotten twin has a different magical ability than Harry. For example, while Harry is good at Defense Against the Dark Arts, the twin might be a natural at Potions or Charms. This could lead to a situation where the twin is initially seen as an outcast in Hogwarts because their skills don't match the typical Gryffindor traits. Another plot twist could be that the forgotten twin was actually hidden away by a powerful dark wizard who planned to use the twin's power for their own evil purposes. This would put the twin in a difficult position when they discover their true past and have to decide whether to side with the forces of good or be influenced by the dark wizard's plans.
One interesting plot twist could be that Hermione and Harry discover their relation much later in their Hogwarts years. Maybe they've always had a special bond but just attributed it to their friendship. Another could be that their shared heritage gives them unique magical abilities that no one else has, like a combined spell -casting power that can defeat the darkest of dark wizards.
One interesting plot twist could be that the twin sisters are the key to a prophecy that involves Edward. They have special powers that are only revealed as the story progresses. This makes them a target for both good and bad forces in the fanfiction world, and Edward has to protect them at all costs.
One interesting plot twist could be that they discover their twin bond gives them shared magical abilities that are unique. For example, they might be able to combine their powers to create a new kind of spell.
One interesting plot twist could be that their different upbringings within the wizarding world lead to a complete role reversal. Harry, raised in the Malfoy family, might be more prejudiced at first, while Draco, having grown up with the Weasleys perhaps, could be more open - minded. This would shatter the initial expectations of their characters and lead to a complex exploration of nature versus nurture in the wizarding world.
Well, perhaps the discovery that the magic system in the Magic Knight Novel is not what it seems at first. Maybe it was thought to be a simple elemental - based magic, but then it's revealed that there's a hidden layer of magic that can only be accessed through a certain rite or by certain people. This could lead to a whole new set of challenges and adventures for the magic knights.
Well, in many magic academy novels, one interesting plot twist could be the discovery that the main character's seemingly ordinary family has a deep connection to the academy's dark secrets. For example, they might be descendants of an ancient and powerful magic family that was banished long ago.
One interesting plot twist could be that the main character, who thought they were infiltrating the secret organization to expose it, discovers that the organization is actually working for a greater good that has been misrepresented. Another could be that a trusted ally within the secret organization turns out to be a double agent working for an even more shadowy group. And sometimes, the secret organization's true purpose is not what it seems at all, like they are not seeking power but rather trying to protect a long - lost knowledge from falling into the wrong hands.
One interesting plot twist could be that one of the partners in the secret marriage is actually from a rival family or organization. For example, in many novels, two business families are in competition, and the secret marriage between a member of one family and the other can create a lot of drama.