One of the most interesting plots might be the Dark One's backstory. How did they become so powerful and dark? In some fanfictions, they were once a normal wizard but a series of tragic events led them down this dark path. This exploration of their origin adds depth to the character and the overall story.
In many 'Harry Potter the Dark One fanfiction' stories, the plot where the Dark One forms an unexpected alliance is really cool. For example, teaming up with some marginalized magical creatures against the Ministry. This completely changes the power dynamics and makes for a very engaging read as it subverts the usual good - vs - evil paradigm.
Well, in some versions, the most interesting plot could be when the Dark One challenges the traditional Hogwarts order. It shakes up the whole wizarding world as we know it from the original books.
Well, Sirius Black can be quite interesting in 'Harry Potter goes dark fanfiction'. If Harry goes dark, Sirius, who has always been a protector figure, might have to make some very difficult choices. He could either try to save Harry from the darkness or be forced to oppose him. Dumbledore is another character that stands out. His wisdom and manipulations would be under a new light in a dark fanfiction. And the Weasley family, especially Ron. His friendship with Harry would be severely tested if Harry goes dark, and his own character development could take some very different paths.
In a lot of these fanfictions, a dark version of Harry himself is very interesting. He breaks away from the traditional heroic mold and becomes a complex character dealing with power, morality, and his own identity. Another interesting character can be Draco Malfoy, who sometimes forms an unlikely alliance with dark Harry, adding more depth to their relationship.
A great plot could involve a portal opening between the two worlds. Harry, Hermione, and Ron accidentally stumble through it. In the Dark Souls world, they find that their magic works differently. They meet characters from Dark Souls who are initially hostile but then realize they have a common enemy in the form of Voldemort's forces that are starting to corrupt the Dark Souls world as well. Harry has to learn the ways of the Dark Souls combat and use his wits and magic to form an alliance. They then return to Hogwarts with new powers and knowledge to face Voldemort in a final battle that combines the magic of Harry Potter and the dark and gritty elements of Dark Souls.
One possible plot idea could be the Dark Prince having a hidden agenda that not even Voldemort is fully aware of. He might be secretly manipulating events to gain ultimate power for himself. For example, he could be using the chaos of the wizarding war to his advantage by making deals with both sides without their knowledge.
Well, in this fanfiction, the plot might revolve around the Dark Prince's secret plans. He could be plotting to overthrow the existing wizarding order. Harry Potter then gets wind of this and has to find a way to stop him. The story could also show how the Dark Prince recruits followers, and what kind of challenges Harry faces in trying to expose and defeat him. There could be a lot of mystery and intrigue as Harry tries to figure out the true motives of the Dark Prince.
One idea could be exploring how the Dark Mark affects the mental state of those who bear it. For example, it might cause nightmares or hallucinations related to Voldemort's will. Another could be a story about a character trying to hide their Dark Mark from their friends in the Order of Phoenix, creating a lot of internal conflict and secrecy.
One idea could be that Harry discovers a dark secret about his family that leads him down a dark path. For example, he might find out that his ancestors were involved in some really evil magic and he starts to explore that side of magic. Another could be that the influence of Voldemort somehow remains and corrupts Harry's mind over time. Maybe the Horcrux inside him wasn't completely removed and it starts to change his way of thinking.
One interesting plot point could be a new, hidden magical power that Harry discovers in this fanfiction. Maybe it's a power that was long forgotten and has some unique connection to his family's past.
One idea could be that Harry, influenced by dark magic, forms an uneasy alliance with Voldemort. They could team up to take over the wizarding world in a different way than Voldemort originally planned, perhaps by ruling jointly. Another plot could involve Harry exploring the darker aspects of his own magic and using some of Voldemort's knowledge to do so, which causes a rift between him and his friends.
One idea could be Harry, as a dark necromancer, using his newfound powers to bring back some of the great wizards from the past to learn from them, but the magic has unforeseen consequences like attracting dark entities. Another could be that he's on a quest to revive a loved one, which goes against the natural order of magic in the wizarding world and causes a rift between him and his friends.