She could be an ancient Celtic goddess, like Brigid. Brigid is associated with magic, healing, and smithcraft in Celtic mythology. In the fanfiction, she might see Harry's potential and decide to train him in her unique magical arts.
The 'Harry betrothed to Lestrange' concept completely rewrites the future of the wizarding world in fanfiction. It can lead to different political alignments. The Ministry of Magic might have to reevaluate how they deal with Harry and the Lestranges. It could also affect the education system at Hogwarts. For example, there might be new classes or teachings related to the Lestrange family's magical practices that Harry brings to light. And of course, it changes the romantic aspect of Harry's life, from his potential relationships with Ginny or others to this new, complex relationship with a Lestrange.
It could be an unknown character who has been in hiding all this time. Maybe she was once a powerful witch who made a pact with death and became its representative in the wizarding world.
Perhaps an interesting concept is how the goddess's presence affects the characters' destinies. In the Harry Potter series, the characters' fates are often tied to the prophecy and the fight against Voldemort. But with a goddess in the fanfiction, her influence could change the course of events. She might offer protection to certain characters, or she could set new challenges that test their loyalty and courage in different ways.
Well, perhaps the goddess could teach Harry some really unique magic that he couldn't learn at Hogwarts. For example, she might show him how to control nature magic in a way that's different from what he's used to. Maybe she trains him to be more in tune with his emotions and use that to power his spells more effectively.
It could be Bellatrix Lestrange's younger sister who was not as involved in the dark arts as Bellatrix. She might be a character who was forced into the shadows because of her family name but has a good heart. Harry's betrothal to her could be a way to redeem the Lestrange name in the eyes of the wizarding world.
The fanfiction could explore the political implications of Harry being betrothed to a Lestrange. It would cause a stir in the wizarding community. Some would see it as a dangerous move, while others might hope it could lead to peace. Harry would have to deal with the public's perception, as well as his own doubts. He may also uncover secrets about the Lestrange family that could change his view of the situation completely. He could be caught between loyalty to his friends who are skeptical and his newfound connection to the Lestrange he is betrothed to.
Sometimes, it could be the pure - blood supremacists. They might not like the idea of Harry, who is a symbol of the fight against them, being betrothed to Fleur, who is part - Veela. They could try to create problems between them.
One common theme is the exploration of their relationship. How they grow from friends to betrothed and then to something more. Another theme is often the challenges they face due to their betrothal, like dealing with the expectations of the wizarding community.
Harry Potter himself is often a main character. Since it's related to the Harry Potter world, he would be in the center of the story most likely. He might interact with the goddess, either as an ally or having some sort of conflict.