One possible plot twist could be that Harry, under Bellatrix's influence, becomes a much darker and more ruthless wizard. Bellatrix might train him in the Dark Arts, and he could end up being a sort of anti - hero. He might have a completely different view of the wizarding world and be at odds with his former friends from Hogwarts.
A major plot twist could be that Bellatrix's love for Voldemort is transferred to Harry in some way. She sees in Harry a potential heir to Voldemort's power or ideology. So, instead of simply being a cruel guardian, she has this complex emotional investment in Harry. This could lead to a situation where Harry has to grapple with this strange form of 'love' from Bellatrix and figure out how it affects his own identity and his relationship with the fight against the Dark Arts.
Perhaps Harry, while being raised by Bellatrix, discovers some long - hidden secrets about his family. Bellatrix, in her own twisted way, might accidentally lead Harry to learn things that Dumbledore had been keeping from him. This could change Harry's understanding of his parents and his role in the wizarding world. He could then use this new - found knowledge to either bring about great change or cause chaos.
Another plot twist could be that Bellatrix realizes she has created a powerful adversary in Harry. As she raises him to be Lord Black, she instills in him a sense of power and ambition. But Harry uses that power not for the dark purposes she intended. Instead, he decides to reform the Black family traditions and bring a new era of inclusiveness to the wizarding world.
One possible plot twist could be that the founders' different teaching styles clash when raising Harry. For example, Salazar Slytherin might be more strict about pure - blood heritage, while Helga Hufflepuff would focus on his kindness. This could lead to internal conflicts within Harry as he tries to balance their different expectations.
One possible plot twist could be that Harry, under Crowley's influence, starts to question the traditional concepts of good and evil in the wizarding world. He might be exposed to dark magic in a different light, not as something purely evil but as a tool with its own uses. This could lead to conflicts with his friends from Hogwarts who adhere to the more conventional views.
The plot could revolve around Harry's struggle to fit in. Since he is a demigod raised by Bellatrix, he is likely to be an outcast in both the wizarding and demigod communities. The wizarding world may not understand his demigod powers and the demigod world may not accept him because of his connection to Bellatrix. He might have to go on a journey to find others like him or to find a place where he truly belongs. Along the way, he could face many challenges and enemies, both magical and perhaps related to his demigod status.
One common plot twist could be that Fem Harry has a much darker personality due to Bellatrix's influence. For example, she might be more prone to using the Dark Arts. Another could be that she has a conflicted relationship with the Order of the Phoenix. Instead of being their ally immediately, she might be suspicious of them because of Bellatrix's teachings. Also, there could be a plot twist where Fem Harry discovers a hidden side of Bellatrix that was not all about the Dark Arts, perhaps a more maternal side that was buried deep within her, which makes Fem Harry question everything she thought she knew about good and evil.
Well, one possibility is that Harry would be raised in a very different magical environment. Bellatrix is a Death Eater, so he might be exposed to dark magic teachings from a young age. But perhaps, deep down, Bellatrix could have some strange maternal feelings towards Harry and protect him from the other more extreme Death Eaters. This could lead to a really complex internal struggle for Harry as he grows up, having to reconcile his own sense of right and wrong with the values he's being taught in Bellatrix's care.
One possible main plot twist could be that Sirius manages to completely hide Harry from the wizarding world's prying eyes until he comes of age. This would mean Harry grows up without the constant threat of Voldemort's followers finding him. Another twist could be that Sirius discovers some long - hidden magic within Harry that was dormant because of his upbringing with the Dursleys, but flourishes under Sirius's care.
One possible plot twist could be that Amelia Bones, being a highly respected figure in the wizarding world, has a secret past that somehow affects Harry's journey. Maybe she was involved in some sort of pre - Voldemort plot that resurfaces when she takes in Harry. This could lead to Harry having to deal with new enemies and allies that are related to Amelia's past.
One possible plot could be Harry growing up believing he is on the right side by following Bellatrix and the Death Eaters. But then he discovers some secrets about his real parents and starts to question everything he's been taught. This leads to an internal struggle as he tries to decide whether to stay with Bellatrix or break away and find his true identity.
Perhaps the biggest plot twist would be Harry's view of the Death Eaters. Growing up with the knowledge that his mother was Bellatrix, he might have a more sympathetic view of some of them at first. He could believe that they were misled rather than inherently evil. This would lead him on a journey to try and reform some of the Death Eaters, which would put him at odds with both the Order and the remaining Death Eaters who don't want to change. It would also change the way we see the divide between good and evil in the wizarding world.