Voldemort would still be a major character. After all, he is Harry's main antagonist. If Harry snaps, it would likely be in relation to his ongoing battle with Voldemort. And the Death Eaters, as Voldemort's followers, would also be involved. They would be on the receiving end of Harry's new, more aggressive stance, and their reactions would shape the story further.
Obviously Tsuna would be the main character. His friends like Gokudera and Yamamoto are likely to be in it too. They might be the ones who are shocked by Tsuna's snapping and try to help him get back to normal. Reborn could also be there as he has been guiding Tsuna all along and would surely play a role in this situation, either trying to understand what made Tsuna snap or trying to fix it.
Harry Potter and Severus Snape are the central figures. However, the other Hogwarts professors could also be important. For instance, McGonagall. She might be the one who tries to calm Harry down after he snaps at Snape or she could be the one who encourages Snape to be more understanding towards Harry. Then there are the Death Eaters. If the fanfiction is set in a context where Voldemort is still a threat, the actions of the Death Eaters could impact the relationship between Harry and Snape. They could be the catalysts that force Harry and Snape to work together and ultimately strengthen their father - son - like bond.
In a 'naruto finally snaps fanfic', Naruto is the main focus, but characters like Kakashi would be involved. Kakashi has been Naruto's teacher and mentor, so he would be affected by Naruto's change. Also, characters from other villages such as Gaara could be part of the story. Gaara has his own connection with Naruto, and Naruto's snapping would have an impact on their relationship and the balance between villages.
Another possibility is that the main antagonist could be the wizarding society as a whole. If Harry has been constantly marginalized or misunderstood by the general wizarding population, he could snap and see them as the enemy. Their narrow - minded views and prejudices, like against half - bloods or Muggle - borns, could be what pushes Harry over the edge. He may then try to change or even rebel against the entire wizarding society.
Well, it could be about Harry finally losing his patience with all the constant threats and dark magic. Maybe he decides to take a more aggressive approach against Voldemort and his Death Eaters, instead of always waiting for them to make the first move.
The main characters would surely include Harry Potter. He's the center of the story as he is the one with the Veela aspect. Ginny Weasley could also be a major character. If Harry is a Veela, it would change their relationship dynamics. Additionally, Dumbledore might play a significant role as he would be guiding Harry through this new discovery and helping him understand and control his Veela powers.
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.