Perhaps their half - human side makes them more attuned to nature magic. So they can draw power from natural elements like trees or rivers in a way that others can't. They could also be part of an ancient prophecy related to their half - human nature, which puts them in the center of a great adventure. And they might have to discover the secrets of their heritage on their own, as there is little knowledge about half - humans in the wizarding community.
One plot idea could be that Hermione is a powerful elf with ancient magic knowledge. She uses her elven abilities to solve mysteries in Hogwarts that normal humans couldn't. Another could be that she's a magical being from a different dimension, and she has to hide her true form while trying to fit in at Hogwarts. Maybe she's a phoenix in human disguise, and she shows her phoenix powers at crucial moments to save her friends.
One idea could be that Harry struggles to control his demonic powers. For example, he might accidentally set things on fire when he gets angry. Another could be that he has to hide his half - demon nature from his friends at Hogwarts, constantly fearing discovery.
They could start by realizing that they are the only ones who understand each other's half - human struggles. This shared experience could bring them closer together. Maybe they have to rely on each other more when facing challenges in the wizarding world that are related to their half - human nature.
Well, perhaps in the fanfiction, there is a prophecy that their unborn child will be the key to a great change in the wizarding world. This makes them a target for both good and bad forces. They struggle with the decision of whether to keep the baby's existence a secret or to embrace it publicly. And as Hermione's pregnancy progresses, they face many challenges, both physical and emotional, as they prepare for parenthood in a world full of magic and danger.
One plot idea could be that Hermione and Harry discover an old, mysterious orphanage during one of their adventures. Inside, they find magical artifacts that are linked to their pasts. Another could be they start an orphanage of their own for wizarding children who have lost their families in the war. It could be a place of learning and safety.
In this type of fanfiction, it might be that Harry has been misled by false prophecies. He kidnaps Hermione thinking he is doing the right thing. As the story unfolds, Hermione uses her intelligence to make Harry see the truth. They then team up to face the real threat that was behind the false prophecies all along. It could also involve a lot of emotional turmoil between the two characters as they deal with the situation, with their friendship being put to the test.
Well, perhaps they have a child who is really interested in Muggle studies, much to the amusement of Harry who has some Muggle - like tendencies. And they struggle a bit with how to balance their child's interest in Muggle things with the wizarding world they live in. Also, there could be a plot where the family has to deal with some old enemies of Harry's who are seeking revenge, but this time they have to protect not just themselves but also their child. It could show how they use their combined skills and knowledge to keep their family safe.
One idea could be that their child discovers a hidden magical ability that neither Harry nor Hermione possess. For example, the ability to communicate with magical creatures in a unique way. Another could be that the child gets into trouble at Hogwarts by accidentally stumbling upon a long - forgotten and dangerous spell.
One idea could be a story where Draco, Harry and Hermione are forced to work together on a special magical project for the Ministry. They start off hating each other but gradually come to respect one another's skills. Another plot could involve them getting trapped in an alternate magical dimension where they have to rely on each other to find their way back. Maybe Draco has some knowledge of the dark magic that created the dimension, Harry has his Gryffindor courage to lead them through dangerous areas, and Hermione uses her vast knowledge to figure out how to break the spell that trapped them.
One idea could be that as siblings, they discover a hidden magical ability that only runs in their family. For example, they might find out they can communicate with magical creatures in a unique way. This could lead them on an adventure to protect these creatures from dark wizards who want to use them for evil purposes.