Another suspect could be a character with a hidden agenda. For example, a wizard from a different magical society who sees Hermione as a threat to their plans. They might have used a very rare and undetectable poison, making it even more difficult for her friends to find a cure and identify the culprit.
There's a possibility it's a follower of Voldemort. Since Hermione is a key figure in the fight against the Dark Lord, they might target her to weaken the opposition. They could have slipped the poison into her drink during a meal in the Great Hall.
It could be a jealous classmate. Maybe someone who is envious of Hermione's intelligence and always being at the top of the class.
It could be Morgana. She has been known to be an antagonist and has a vendetta against Camelot and those associated with it. Poisoning Merlin would be a way to weaken Arthur's most powerful ally.
Perhaps an enemy from a rival group. They might see Sakura as a threat to their plans, so they poison her to get her out of the way. Another possibility is a character who has been secretly harboring a grudge against her for a long time, and finally decides to take action by poisoning her.
It could be Orochimaru. He's always been interested in obtaining powerful bodies for his experiments. Naruto's body, with the Nine - Tails' power, would be a great target for him.
It could be Draco Malfoy. He has had a long - standing rivalry with Harry. Maybe in this fanfic, he finally decides to take extreme measures out of envy or pressure from his family.
It could be a jealous student. Maybe someone who has a crush on the same person Harry is attracted to in the story. They see Harry as a rival and figure that by poisoning him with a love potion, they can make him look foolish or get him into trouble.
It could be a disgruntled house - elf. Maybe one that was mistreated by its wizarding family and decided to steal money as revenge. They could use their magic to get into places unnoticed and take the money.
It could be an old enemy of the Hyuga clan. Since Hinata is a part of the Hyuga, someone with a vendetta against the clan might target her.
Hermione might also come across some magical creatures that are guarding certain vaults in Gringotts. For example, a dragon that she has to find a way to bypass without getting burned. These encounters would add more excitement and danger to her visit to the wizarding bank.
There might be Muggle soldiers who are initially skeptical of Hermione but later become her allies. She could also meet some higher - up military officials who either support or oppose her presence in the army. For instance, a general who sees the potential in Hermione's magical abilities and wants to utilize them for the greater good, or a colonel who is against having a witch in the military due to traditional beliefs.
Definitely fans of Hermione herself. If they've always been intrigued by her character and wanted to see her in a more unique and out - of - the - box situation, this fanfiction would be right up their alley. Additionally, those who are into speculative fiction, where characters are taken out of their normal settings and given new traits, would likely be interested in a story where Hermione is a mutant.