In this fanfiction, perhaps Hermione uses her vast knowledge of magic. She might save the Weasleys from a dark wizard's attack. Maybe she discovers a powerful spell to counter a curse aimed at the Weasley family.
Well, it could be that the Weasleys are in some sort of financial or magical disaster. Hermione, with her quick thinking and intelligence, figures out a solution. For example, she could find a way to restore their crumbling magical home or solve a problem with their magic - based business. She is known for her problem - solving skills in the original series, and this would be an extension of that in the fanfiction.
Well, it could be a completely innocent and humorous story. Maybe they all got accidentally locked in a magically malfunctioning shower room at Hogwarts. And they have to work together to get out, with Hermione using her intelligence and the Weasleys' unique skills and prank - like ideas. It could be full of banter and light - hearted moments as they figure out a solution.
One possible plot could be that the Weasleys might betray Hermione over a powerful magical artifact. Maybe they believe she has become too power - hungry in her pursuit of knowledge about it and they side with those who want to keep it away from her.
In the fanfiction, it could start with Hermione having a falling - out with her own family due to her magic. The Weasleys, seeing her distress, offer to adopt her. As a part of the Weasley family, Hermione would be involved in all their family traditions. She could bring her intelligence to help with family matters, like helping with George's business by using her logical thinking. And her relationship with Ginny would become even closer, like true sisters, sharing secrets and having girl - talk that they didn't have much opportunity for before.
One possible reason could be a misunderstanding. Maybe there was a miscommunication about something important, like a plan to fight against the Dark Arts. For example, if the Weasleys accidentally left Hermione out of a crucial part of the plan, she might be very angry.
Obviously, Hermione and the Weasleys. Hermione is the one doing the saving, so she is the central character. The Weasleys as a whole family would also be important, including characters like Molly, Arthur, Ron, Ginny and the others.
Well, it could be that Hermione uses her time - turning device to go back in time and warn the Potters about Voldemort's plan. Maybe she disguises herself and manages to get into their hiding place, then uses her magic skills to set up powerful protective spells around them that Voldemort can't break through.
Rather than focusing on such improper fanfiction, it's better to explore the positive and official stories in the 'Harry Potter' universe, like Hermione's friendship with the Weasleys in the proper context.
One possible plot could be that Hermione stumbles upon Fenrir Greyback in a situation where he's about to be killed by some dark wizards who see him as a loose end. Hermione, being the empathetic and brave witch she is, decides to save him. Maybe she believes that every life is worth saving, even a werewolf like Fenrir. She could then try to rehabilitate him, using her vast knowledge of magic and her strong moral compass.
Perhaps in the fanfiction, Cormac invites Hermione to a secret gathering, but his intentions are not so noble. Ron finds out and races to the location to save Hermione. This act of heroism by Ron might make Hermione question her feelings for him. She might start to see him as more than just a friend, especially if Ron shows a side of himself that she hasn't fully appreciated before. The story could then follow how their relationship evolves from this event.
In this fanfiction, it could be that Ron is under the control of a powerful wizard who wants to get to Hermione for some reason. Charlie discovers this plot and decides to protect Hermione. He sets up various traps and wards around the place where Hermione is staying. When Ron, being controlled, tries to attack Hermione, Charlie is there to intercept him, engaging in a magical duel if necessary to save Hermione.