A potential new character could be an old hermit who has been living in seclusion for centuries, having mastered the Dark Arts long ago. He becomes Harry's mentor in the Dark Arts, teaching him secrets that have been lost to the wizarding world. There could also be a group of outcast wizards who have been wrongly accused of misusing the Dark Arts. They approach Harry and offer their knowledge and help, which adds new layers of conflict and cooperation in the story.
There could be a dark arts teacher who is actually a double - agent. This character might seem to be teaching Harry the wrong things at first but is actually guiding him to use the Dark Arts for good. Another new character could be a mysterious figure from an ancient dark arts cult who tries to recruit Harry for their own purposes.
Bellatrix Lestrange could be a potential focus as a dark arts master in fanfiction. She already has a deep knowledge of the dark arts in the original series. Fanfiction could explore her even more, perhaps showing her training others in the dark arts in a more in - depth way.
There could be a wise old wizard who has knowledge about the true nature of the Master of Death and becomes Harry's mentor. Maybe a powerful magical creature that is drawn to Harry's power and offers its assistance.
Another potential set of new characters could be ancient wizards or witches who were once associated with the concept of the master of death. They could come back to either guide Harry or challenge his claim to the title. This would add a lot of depth to the story as Harry would have to prove himself to these predecessors or learn from their experiences.
One potential consequence could be a change in his relationships. His friends might be worried or even turn against him. For example, Hermione, who is always concerned about following the rules and doing what's right, would likely be very troubled. Another consequence could be a shift in his own moral compass. The dark arts are often associated with negative and unethical actions, so he could start to make more morally ambiguous decisions.
There could be an American wizard who takes Harry under his wing, like a gruff but kind old wizard named Alistair. He could teach Harry about American magic in a no - nonsense way.
Hermione could be a likely character. In the original series, she was always by Harry's side. In this fanfiction, her intelligence could be a great complement to Harry's 'dark godlike' powers. Ginny Weasley is also a possibility, given her connection to Harry in the official story. And Luna Lovegood might be included too, with her unique perspective adding an interesting flavor to the harem dynamic.
Hermione could be one of the characters in the harem. Her intelligence would be an asset to Harry, even as a Dark Lord. She might be torn between her loyalty to the original Harry she knew and her feelings for this new, darker version. Ginny could also be part of it. Given her connection to Harry in the original story, her presence in the harem could add an interesting dynamic, especially if she tries to change Harry back to his old self.
A less obvious candidate could be a corrupted Dumbledore. Imagine if he was swayed by the allure of absolute power and became the dark king. It would be a huge twist as he is seen as a symbol of good in the original books.
One potential new character could be an old hermit - like wizard who has been living in the woods near the manor. He has a deep connection with the land on which the manor stands and can communicate with the spirits of the forest. He could be a source of ancient wisdom for the main characters. Also, a young and adventurous witch who is on a quest to find a lost magical gem that is rumored to be hidden somewhere in the manor. She could bring a new dynamic to the group with her fearless and independent nature. There could also be a magical gardener who takes care of the manor's enchanted gardens and has some secrets of his own.
It could also be an existing character from the Harry Potter series like Hagrid. Given his love for all creatures, including some that are considered dangerous, he could be at the center of a story about the 'Lord of Dark Creatures'. He might be trying to protect these creatures from those who would use them for evil purposes or trying to rehabilitate them.