Hermione would definitely be important. She could use her extensive knowledge to help Harry understand his creature inheritance. For example, she might research ancient texts to find out more about the origin of his inherited traits.
A new character, an old and wise creature who has knowledge about the type of inheritance Harry has, could be introduced. This character could act as a mentor, teaching Harry about the history and significance of his inheritance, and guiding him on how to use his new abilities for good.
In this kind of fanfiction, creature inheritance often works through family bloodlines. If a family has a long - ago connection to a certain creature, like an ancestor who made a pact with a unicorn, that connection might be passed down generations. It could also be triggered by a magical event. For instance, if a character is in a place where a powerful magical creature once lived and a magical energy is released, it could awaken the inheritance.
Hermione would surely play an important role. She could help Harry figure out the details of his inheritance, like deciphering old documents or researching the history behind it.
It's hard to say without reading it, but it could be the main trio - Harry, Hermione, and Ron. They often get involved in all kinds of magical situations in fanfiction.
Draco Malfoy can be a key character too. Maybe he inherits the pride and territorial nature of a dragon - like creature. This would add an interesting dimension to his character, as he would have to deal with this new part of himself while also navigating his family's expectations and his own place in the wizarding world.
Harry Potter himself is often a central character in such fanfictions. Given his connection to various magical creatures throughout the original series, it's not a stretch to imagine him inheriting something related to a rare creature. Hermione could also be a common character. Her thirst for knowledge might lead her to discover or be involved in a rare creature inheritance. Ron, with his Gryffindor bravery, might also be in the mix, perhaps inheriting a trait from a more combat - related rare creature.
There could be new characters introduced as well. For example, an old wizard or witch who has knowledge about the specific creature inheritance Harry has. They could be a mentor figure, teaching Harry how to control and use his newfound abilities. And of course, the antagonists like Voldemort would be affected by Harry's new powers. They might try to find a way to counter or steal Harry's creature inheritance powers.
Well, obviously Harry himself is the central character. But aside from his friends, characters like Draco Malfoy could have a different relationship with Harry. Instead of being just a rival, he could be an ally of sorts in Harry's dark journey, or perhaps he tries to use Harry's newfound darkness for his own gain. Snape too could be important. Given his complex relationship with Harry, he might be in a position where he has to choose between helping Harry return to the light or letting him continue down the dark path.
Hermione would definitely be an important character. She's smart and resourceful, so she'd be the one researching ways to restore Harry's memory. Ron would also be crucial as he's Harry's loyal friend. He'd be there to support Harry and keep him out of trouble. Dumbledore or other wise Hogwarts professors like McGonagall could also play significant roles. Dumbledore might have some secret knowledge or plan to help Harry, and McGonagall could provide guidance and protection at Hogwarts.
Neville could play an interesting role. Maybe he could be the one who discovers a new magical plant that is needed for a potion to cure an illness that Ginny or Harry contracts during their marriage. Luna could also be involved. She might come to them with some strange but useful prophecies that help them in a difficult situation, like dealing with a dark wizard who has a grudge against Harry even after the war is over.
One possible fanfiction could be about a female character who discovers she has a unique creature inheritance in the Harry Potter world. Maybe she finds out she has Veela blood, which gives her an alluring charm. This could lead to various plotlines, like dealing with unwanted attention at Hogwarts or using her charm to her advantage in magical duels.