Another possible main character could be a new villain. Since Harry is in a new role as an apprentice, there could be someone who wants to steal the secrets of Ollivander's wand - making. This villain could be a dark wizard or a rogue wizard who has his own motives for wanting to control the wand - making process. Harry would then have to protect Ollivander and the shop from this threat.
Maybe the story could revolve around Harry being Ollivander's apprentice during a time of great danger in the wizarding world. As an apprentice, he has access to Ollivander's secrets and knowledge. He uses this to his advantage when fighting against dark forces. For example, he might learn how to repair broken wands quickly, which becomes a crucial skill during battles when wands are often damaged.
In 'harry is an apprentice fanfiction', apart from Harry, there might be other apprentices too. They could be his friends or rivals during his apprenticeship. Also, we can't rule out the appearance of some of the main antagonists from the original series, as they might try to interfere with Harry's apprenticeship journey.
The apprentice is obviously one of the main characters. They are likely to be a young wizard or witch with great potential. Then there might be characters representing the different houses of Hogwarts, like a descendant of Gryffindor who is a mentor to the apprentice. There could also be a rival apprentice who has different ideas about the founders' magic.
Obviously, Naruto and Hiruzen would be the main characters. Naruto as the apprentice and Hiruzen as the mentor.
Obviously, Naruto and Anko would be the main characters. Naruto, the energetic and determined ninja, and Anko, the somewhat eccentric and skilled kunoichi.
Obviously, Harry Potter would be one of the main characters. And Naga Sadow, as the one Harry is apprenticed to. There might also be some of Harry's friends from Hogwarts like Hermione and Ron, who could be trying to bring him back from the dark path he's on.
In this kind of fanfiction, Neville Longbottom could also emerge as a key character. He has shown great courage and growth throughout the Harry Potter series. When Hera enters the picture, Neville could be the one who has an unexpected connection with her. Maybe his family's long - forgotten magical heritage has some link to the Greek mythology that Hera represents. And then there are the Death Eaters. If the story is set during the darker times in the wizarding world, the Death Eaters might see Hera as a new threat or a potential ally, making them important characters in the fanfiction as well.
Obviously, Harry Potter would be one of the main characters. He's the central figure in the original series. And Ophis, as the other part of the fanfiction's title, would also be a main character. Her unique abilities and personality would play a big role. Hermione and Ron could also be important as they are Harry's closest friends and would be involved in any new adventures that come about due to Ophis's presence.
Harry Potter himself could still be a main character. He has faced many enemies and situations where he has to make tough decisions. In a 'no forgiveness' scenario, he might be more hardened and less likely to give second chances. For example, when dealing with Voldemort's followers, he could be more ruthless.
Definitely characters from both 'Charmed' and 'Harry Potter'. From 'Harry Potter', Harry, Hermione, and Ron are very likely to be main characters as they are the central figures in the original series. In 'Charmed', the Halliwell sisters, Prue, Piper, and Phoebe, would be prime candidates. Their different powers and personalities would create interesting dynamics when interacting with the 'Harry Potter' characters.