Well, a great plotline might be Harry delving into the history of Slytherin. He could discover secrets about the founder that give him an edge in leading the house. For example, he might find hidden chambers or spells that only the true heir of Slytherin should know. This could lead to him using this knowledge to protect Slytherin students from discrimination and also to gain respect within the wizarding world as a Slytherin leader.
One possible plotline could be Harry using his new position to reform Slytherin house. He might change the way Slytherins are perceived in Hogwarts, promoting unity among all the houses.
One interesting plotline could be the exploration of the Slytherin Prince's backstory. Maybe he has a hidden family legacy or a past encounter that shaped his personality. Another could be his relationships within Slytherin house, like rivalries or unexpected friendships. Also, his interactions with Harry Potter in a different light than in the original books, perhaps as an ally in some situations rather than an enemy.
Another plotline could involve a Slytherin student who is constantly trying to break free from the negative stereotypes associated with their house. They use their Slytherin heritage in positive ways, like being cunning in solving mysteries that are plaguing the school, and in the process, they change the perception of Slytherin within the Hogwarts community.
One interesting plotline could be the exploration of the true identity of the Heir of Slytherin. Maybe it's not who everyone suspects. For example, it could be a character who has been hiding their Slytherin heritage all along.
One interesting plotline could be the main character's struggle to fit in Slytherin while still holding onto some of the values Harry Potter himself represents. Maybe they're trying to change the perception of Slytherin from within.
One possible plotline could be Harry struggling to fit in at first. He's known for being a Gryffindor, so in Slytherin he'd face prejudice from both houses. Another could be him befriending Draco Malfoy early on and changing Draco's views. He might also discover a hidden side of Slytherin's history that helps him in his fight against Voldemort.
Perhaps there could be a plot where Harry discovers ancient Slytherin magic that only the heir can access. This could lead to him having to make difficult choices between using this power for good or being corrupted by it. He may also have to deal with the Slytherin house's expectations of him as their heir, which are quite different from what he has known in Gryffindor.
One interesting plotline could be how the concept of 'King of Darkness' changes the power dynamics in the wizarding world. For example, Harry might have new and unexpected magical abilities that set him apart from the original story. Another could be his relationships with other characters. Maybe he forms new alliances or has different rivalries. It could also explore how the wizarding world reacts to this new, darker version of Harry.
In some 'harry potter dark king fanfiction', there could be a plotline where the dark king has a hidden agenda related to ancient magic. He might be searching for a powerful, long - lost spell or artifact that could give him ultimate control over the wizarding world, and Harry Potter and his friends have to stop him.
Well, a plotline could involve Harry Potter using his unique connection with the characters in the harem to gain new magical knowledge or powers. Maybe one of the harem members has a special family magic that Harry discovers and is able to incorporate into his own skills, all while trying to keep the peace and harmony within the group.