It might be an unknown wizard who is under the control of a powerful dark magic. This wizard doesn't really have his own will but is acting on the commands of the dark force, which sees Hermione as a threat to its plans.
Well, perhaps it's part of a rescue mission gone wrong. She's pushed up against the porthole while trying to escape from some dark wizards. Her friends are nearby but are preoccupied with fending off other threats. She might be using the porthole as a vantage point to look for an escape route or a way to signal for help.
Perhaps a wizard from a foreign magical school who is jealous of Hogwarts' reputation and believes that by kidnapping Hermione, he can undermine Hogwarts. He may think that her abduction will cause chaos and damage the school's standing in the wizarding world. Also, it could be a magical being that has been corrupted by dark magic and views Hermione as a threat to its new - found power, so it takes her away.
An old - fashioned pure - blood wizard who doesn't like Hermione's Muggle - born status. He sees her as an outsider and wants to make her life difficult at Hogwarts. He uses a charm that causes water to seep through her clothes whenever she enters certain areas of the castle. This is his way of trying to drive her out of Hogwarts.
Some dark wizards or witches who oppose the new order at Hogwarts after the fall of Voldemort could also be the villains. They might see Hermione as a threat to their plans of taking over or causing chaos in the wizarding world. They could force her to do things against her will in order to gain an advantage over the good side.
She could interact with Tsuna. Maybe she is initially hired to target him, but as she gets to know him, she realizes he's not what she expected and ends up helping him instead.
One possible reason could be a moment of intense emotion. Maybe Draco is frustrated with Hermione's success or her constant opposition to his ideas in the wizarding world. It could also be a misinterpretation of feelings. For example, he might actually have some hidden admiration for her but doesn't know how to express it in a positive way, so it comes out as this aggressive action. Another aspect could be related to the overarching plot of the fanfiction world. Perhaps there's a power struggle or a mystery that involves both of them, and this physical act is a turning point in the story.
It could be a dark wizard or witch who wants to harm her. Maybe they see her as a threat to their evil plans, so they use a bite as a form of attack. It could also be a misunderstood magical creature that was provoked or scared.
One possible plot could be that she's caught in a sudden rainstorm during a crucial moment, like when she's on a mission to find a hidden magical object. The rain soaks her, and she's frustrated because it might ruin the parchment with the clues she has. And she can't use a spell to dry off immediately as it might draw unwanted attention from dark forces in the area.
Well, Harry Potter is likely to be one of the main characters. He's always been an important part of Hermione's life in the original series, and in this fanfic, he might play a crucial role in the events related to the Half - Blood Prince. Maybe he and Hermione are on a joint mission to uncover the secrets of the Half - Blood Prince.
However, she would still retain some of her old self. Her love for knowledge might lead her to study different ways of being a hitman. And she would probably still feel guilty when she has to do something morally ambiguous, unlike a typical cold - blooded hitman.