It could be an ancient and powerful dark wizard who has been dormant for a long time. Maybe someone from the time before Hogwarts was even founded.
Perhaps it's a character who was once a hero but was corrupted by dark magic. He could be a former Hogwarts student who dabbled too deeply in the dark arts and became the 'Prince of Darkness'. There could be a whole backstory about his fall from grace and how he now poses a threat to the wizarding world again.
In this fanfiction, the 'Prince of Darkness' might be a new character entirely, created specifically for this story. He could be a being from a different dimension or realm, bringing with him powers and knowledge that are completely alien to the wizarding world of Harry Potter. His arrival could disrupt the balance between light and dark magic, and Harry Potter would be at the center of the conflict to either stop him or understand his purpose.
Perhaps it could be a corrupted version of one of the existing characters. For example, a character who has been influenced by dark magic and has turned into this 'prince of darkness'. It could be a Slytherin student who has delved too deep into the forbidden knowledge of the house and has become a dark force. Another possibility is that it's a long - lost relative of a major villain like Voldemort, carrying on his legacy in a new and terrifying way.
It could be a new villain that the fanfiction author has introduced. Maybe a long - lost relative of Voldemort who has emerged to continue his dark legacy.
It depends on various factors. Some fanfiction works gain popularity within specific fan communities. 'Harry Potter' has a huge fan base, but a 'Prince of Darkness' - themed fanfiction might be popular among those who like darker, more alternative takes on the story. However, it may not be as mainstream as some other more canon - compliant fanfics.
In Harry Potter fanfiction, 'The Prince of Darkness' could refer to a number of things. It might be a new character created by the fanfiction writer, perhaps a dark wizard or a powerful, malevolent being. It could also be a title given to an existing character in a new, dark context, like Voldemort being given this title to emphasize his extreme evilness.
Maybe it could be about a character, perhaps Harry himself, being corrupted and turning into a 'Prince of Darkness'. He could start using dark magic and turn against his friends and Hogwarts.
Many of the powerful noble houses would be his enemies. For example, the Lannisters, who are already in a struggle for power. They would not want to share or lose their power to the Prince of Darkness. And the Tyrells, who are also politically astute and would view the Prince as a threat to their influence and the stability of the Seven Kingdoms.
I'm not sure specifically as there could be many different takes in a fanfic with that title. It might be about a character in the Harry Potter universe who is seen as the 'prince of darkness', perhaps a new villain or a dark interpretation of an existing character.
In some 'prince of darkness harry potter fanfiction', there might be a plotline where the 'Prince of Darkness' is a misunderstood figure. He may have been misjudged by the wizarding community for centuries. And now, through his interactions with Harry Potter, his true nature and motives start to be revealed. This could lead to a situation where Harry has to decide whether to trust him or not, and it could also cause a rift between Harry and his friends who might be more suspicious of the 'Prince of Darkness'.
Some of the teachers at U.A. might also be antagonists. They could be secretly working for an organization that wants to control Izuku's powers for their own evil purposes. They would pretend to be helpful while actually setting traps and spreading misinformation about him.
The obvious choice would be the Prince of Darkness himself. He could be a powerful being with the ability to manipulate shadows and dark magic, constantly trying to draw Percy to the dark side.