Perhaps a plot where Orion has to face his inner fears represented by the dark. It could involve him having to make difficult choices to overcome the darkness that surrounds him. He might find allies along the way who teach him how to control the power of the dark rather than be consumed by it.
Obviously, Orion is one of the main characters. He is likely at the center of the story's events.
One interesting plot could be Harry, now as Orion Black, using his knowledge from his previous life to change the fate of the Black family. He might try to prevent some of the dark deeds the family was involved in. Another could be his interactions with the younger versions of characters he knew before, like Snape or Sirius. It would be really fascinating to see how he navigates the wizarding world with this new identity and old memories.
One interesting plot could be the dark prince's struggle with his inner darkness. Maybe he has to make a choice between following his dark instincts or a path of redemption. For example, he meets a character who shows him kindness and makes him question his ways.
Well, in some 'Hermione and Harry Dark Fanfiction', there might be a plot where they enter a dark, alternate magical realm. In this realm, they have to rely on their friendship and skills in new ways. They could encounter dark versions of their friends and have to fight against them, which would really test their loyalty to each other.
One interesting plot could be Naruto getting trapped in the SAO world and having to use his ninja skills in a virtual setting. For example, his shadow clone jutsu could be used in unique ways to overcome challenges in the game, like sending clones to explore different areas of the virtual world simultaneously.
One interesting plot could be the Dark King's struggle against an ancient evil that threatens his realm. Maybe he has to gather allies from different corners of his kingdom, some of whom are reluctant at first but later come to see the importance of the fight.
Another plot could be a twist in the magic system. Suppose one of the sisters discovers a new form of magic that was previously unknown. This new magic could either give her an edge in the competition or force the other sisters to adapt and learn it as well. It could also attract the attention of dark forces or ancient entities that have their own agendas regarding the queenship.
One interesting plot could be the Dark Prince having to face his inner demons while trying to protect Hogwarts. Maybe he discovers a new, dark magic that he must either control or destroy.
One interesting plot could be the exploration of a darker side of the Naruto universe where the main characters face moral dilemmas they never had to in the original series. For example, Naruto might have to make tough choices between saving his friends and sacrificing his own principles in the 'dark empire' setting.
Perhaps there's a prophecy that the others know about and they believe that by keeping Harry in the dark, they can change the outcome. They might think that if Harry knows the details of the prophecy, he'll act in a way that will lead to a bad end, so they're trying to manipulate events from behind the scenes without his knowledge.