He might initially show annoyance. After all, Hermione is often seen as a know - it - all in his eyes. But his sense of justice and his underlying good nature (despite his cold exterior) would kick in. He'd untie her in a rather brusque manner, but then start to question her about how she got into this mess. Depending on her answer, he might offer some cryptic advice on how to avoid similar situations in the future.
One possible plot could be that Hermione was set up by some dark wizards who wanted to use her as bait to lure in Harry Potter or other members of the Order of the Phoenix. Snape, being a double agent, stumbles upon her while on one of his secret missions. He might initially be conflicted between his loyalty to the Death Eaters (on the surface) and his true allegiance. He decides to help Hermione, using his knowledge of dark magic to free her from the bindings and then they have to work together to escape the place before the real villains return.
Fleur could be a bit hesitant at first, not fully understanding the situation. But once she realizes the gravity of Hermione's state, she becomes determined. She might call for help from other reliable wizards or witches she knows. Fleur would also comfort Hermione, telling her that she's safe now and that they will find the culprits. She may use her Veela charm in a subdued way to soothe Hermione's distress.
Well, fanfiction involving such scenarios can be a bit of a grey area ethically. On one hand, if it's done in a non - malicious and non - sexual way, it could be seen as exploring different plot ideas within the fanfiction world. However, if it has any undertones of harm or inappropriate behavior, it's not okay. Many people might find it disturbing or against the spirit of the original characters.
Snape might be suspicious at first. He might think it's some sort of trick or part of a bigger plot. However, as he observes Hermione more closely and realizes the genuineness of her situation, his attitude could gradually change to one of reluctant assistance. He might even offer some words of wisdom, albeit in his typical sarcastic way, to help Hermione regain her strength.
Often, there's a theme of friendship and loyalty. Her friends, like Harry and Ron, will usually come to her rescue. And also, the theme of magic. There are often magical elements that are either the cause of her being tied up, like a cursed spell, or the solution to her getting free. In some cases, it can also be about self - discovery. Being in such a tough situation makes Hermione realize new things about herself and her abilities.
It's often for the sake of creating drama. Tying up a main character like Hermione puts her in a vulnerable position, which can drive the plot forward. It makes readers worry about her and wonder how she'll get out of the situation.
The theme of danger and rescue is also quite common. Hermione being in a vulnerable state of being tied up often leads to a situation where her friends or allies need to rescue her. This builds up the tension and shows the loyalty within the group.
A common theme could be redemption. Snape, who has a complex and often - dark past, might find in Hermione a chance to redeem himself in some way. Maybe he saves her from a danger in the dungeon, which starts his journey towards a more positive path. Another theme is the exploration of hidden knowledge. The dungeon is full of secrets, and both Snape and Hermione are curious minds. They could uncover something that changes their understanding of Hogwarts or the wizarding world.
One plotline could be that they are victims of a prank by some mischievous students using a new, untested spell. They then have to figure out how to break free and also how to deal with the fallout of being in such an embarrassing situation together.