Dumbledore could also play a role, guiding Harry in how to use his new position for the greater good. And then there might be members of the Ministry of Magic who are either supportive or skeptical of Harry becoming a lord. Some pure - blood families might also be involved, either trying to befriend Harry for his new status or plotting against him.
There could be new characters introduced, like old family retainers of the noble family Harry is now part of. Maybe an old wizard who serves as an advisor to Harry on matters of the lordship. And of course, some antagonists such as rival lords or wizards who don't want Harry to gain too much power.
The Order of the Phoenix would be likely antagonists. Since Harry has turned to the dark side, they would see him as a threat to the peace and safety of the wizarding world. Dumbledore, if he were still alive in the fanfiction, would also oppose Harry. He would try to use his wisdom and power to bring Harry back to the light. Another antagonist could be Neville Longbottom. Neville, who has always been a symbol of resistance against the dark side, would not stand for Harry becoming a dark lord and would fight against him to protect Hogwarts and the values it stands for.
Obviously, Albus would be one of the main characters as the title implies he is the one who 'becomes' like Harry. And Harry himself would also be a central figure, either as a sort of inspiration or even in flashbacks.
In 'harry becomes lord potter at 7 fanfiction', Harry is the main character, but there could be other important characters too. Maybe there are some members of the Potter family's old allies who come forward to help Harry. For example, the Longbottoms could be important as they have a long - standing relationship with the Potters. And then there might be some antagonists, like the Malfoys, who could be envious or try to undermine Harry because of his new title.
Hermione is often present. She might help Harry understand the legal and political implications of his new lordship. Ron would also be there, probably as Harry's loyal friend, providing support and some comic relief. Dumbledore could still play a role, perhaps as a mentor guiding Harry in how to use his new power for the greater good.
Hermione would likely be one of the main characters. She's always been Harry's intelligent and resourceful friend. In this fanfiction, she could use her vast knowledge of magic to help Harry on his journey to becoming a powerful lord. For instance, she might research ancient texts to find spells that can enhance Harry's power.
Hermione would surely be one of the main characters interacting with Harry. She might try to bring him back from the dark side, constantly arguing with him about his choices and trying to remind him of their old friendship and the good they used to fight for.
Ron is also there. He could be Harry's right - hand man in some adventures related to his lordship. For example, when Harry has to deal with some dark wizards threatening his lands, Ron might be by his side, using his Weasley - family - taught magic skills.
Obviously, Harry Potter himself would be one of the main characters. Since it's about his connection to the Lord Black trial. Sirius Black's presence might also be felt strongly, even if not physically present, as his past and the Black family's reputation are central to the trial. Hermione and Ron would most likely be there too, as Harry's closest friends, providing support and using their intelligence and skills to help Harry through the trial.
Obviously, Harry Potter himself is a main character. Since he is becoming Lord Potter, he is at the center of the story. Hermione and Ron are likely to be important characters as well, as they are Harry's closest friends and will surely be involved in his new journey as Lord Potter.
Obviously, Nightwing himself would be the main character as he's the one taking on the Batman role. Robin, if there's a younger Robin at the time in the fanfiction, would also be a key character. He might look up to Nightwing in his new role or have some doubts about him filling Batman's shoes.