Well, in this fanfiction, it could be that the 'dark' entities that rescue Harry have a hidden agenda. They might think that Harry has the potential to be a powerful ally in their fight against the established order. It could also be a story about redemption for the dark side, where rescuing Harry is the first step in a journey to change the way things are in the wizarding world. This might involve a lot of character development for both Harry and the dark characters involved.
Obviously, Harry is one of the main characters since the title mentions he is being rescued. As for the 'dark' side, it could be Voldemort or some of his Death Eaters, or perhaps some other dark - themed original characters created for the fanfiction.
Harry is the main human character. Among the vampires, there could be a vampire who was once a wizard and turned into a vampire. This character would have a unique perspective as he understands both worlds. There might also be a vampire hunter who has a change of heart and ends up helping the vampires rescue Harry. All of these characters would interact and drive the story forward in the fanfiction.
In the fanfiction world, Greengrass is often a Slytherin student. She usually comes from a pure - blood family, which gives her certain status and expectations within the wizarding world. In the context of rescuing Harry Potter, she might be a character with a strong sense of justice that goes against the typical Slytherin stereotype. She could have her own set of skills, like being an excellent duellist or having a deep understanding of certain types of magic that enable her to come to Harry's aid.
This fanfiction might revolve around the idea of Harry being in a dire situation where he is being abused. Lucius, for some reason, decides to rescue him. It could be set in an alternate universe where the normal power dynamics and relationships are shifted. The story might delve into how Harry copes with the aftermath of the abuse and his new relationship with Lucius, whether it's one of mistrust at first or a strange alliance.
One possible plotline could be that the vampires, despite their dark nature, are drawn to Harry's unique magical aura. They see him as a key to some greater power or mystery in the wizarding world and rescue him from a dangerous situation, like a dark wizard's lair. Then, Harry has to navigate his new relationship with these vampires while also dealing with the implications it has on his standing in the wizarding community.
One common theme is the clash of different worlds. For example, when Harry Potter is rescued in a crossover with another universe, like the Star Wars universe, there's a lot of focus on how the magic of Harry's world interacts with the technology and different species in Star Wars. It's about two very different concepts trying to coexist.
One possible plot could be that Harry is wrongly accused of a crime in the wizarding world, perhaps something related to dark magic. The police, who might be a new magical law enforcement unit, rescue him from an angry mob. They then help him clear his name by finding the real culprit, who could be a Death Eater in disguise trying to frame Harry to cause chaos in the post - Voldemort era.
Perhaps there is a prophecy in both universes that foretells of a great danger that only the combined forces of Harry Potter and the Avengers can face. When the Avengers learn of this, they travel to the wizarding world to find Harry. They rescue him from an immediate threat so that they can all prepare to face this greater danger together. The Avengers could introduce new ways of fighting and thinking to Harry, while Harry could share his knowledge of magic with them.
In a 'Harry sold rescued Snape' fanfiction, the plot could start with Harry learning that Snape is held captive by a group of dark wizards. Harry realizes that he needs certain magical supplies or potions to break Snape free. Since he doesn't have the funds to buy these items, he decides to sell a rare spell book that he found in the Room of Requirement. This spell book has some unique spells that could potentially be used against the dark wizards. But once he sells it, he discovers that the buyer has some ulterior motives and is somehow connected to the group holding Snape. Now Harry has to not only get the spell book back but also figure out how to use it to rescue Snape while dealing with the new threats that have emerged.