Some fanfictions play on the idea of jealousy. If Harry starts to gain more fame or power than the Weasleys, especially Ron, it could be a reason for them to betray him in the fanfiction. But this goes against the real friendship and support they showed in the books, where they were always proud of Harry's achievements.
A plot could involve a family secret. Maybe the Weasleys discover that Harry has some connection to an event in their past that they wrongly interpret as harmful, and this leads to their betrayal. For example, if they think Harry is related to someone who caused harm to their family long ago, even though it's a false connection.
Another possibility is a miscommunication or false accusation within the fanfiction world. Someone could spread lies about Harry among the Weasleys, leading them to believe he has done something terrible and thus turning against him. But this is a far cry from the deep bond they share in the official 'Harry Potter' story.
Well, in some fanfictions, it could be that the Weasleys betray Harry because of Voldemort's influence. Maybe they are Imperiused to turn against him.
A common plot is the misinterpretation of Harry's actions. His friends might think he's being secretive about something dangerous, like a new form of magic he's discovered, when in fact he's just trying to protect them. Another plot could be that a new character enters the story and manipulates his friends against Harry for their own gain.
A common plot is that Dumbledore has been manipulating Harry from the start. He might have arranged events in Harry's life to lead him to a specific fate against Harry's will. For example, making sure Harry attended Hogwarts to be part of the fight against Voldemort.
In this fanfiction, the betrayal might also stem from jealousy. Harry is often in the spotlight, and the Weasleys, who have always been a big family but not always in the center of attention, could let envy get the better of them. This could lead to actions that Harry perceives as betrayal, like spreading rumors or withholding support when he needs it most.
Love could also play a role. Maybe one of the Weasleys falls in love with someone who has a vendetta against Harry. To please their love interest, they could end up betraying Harry. It's a more emotional and complex reason compared to the others, but it can add depth to the fanfiction story.
Well, in some fem Harry betrayed fanfictions, the betrayal often stems from jealousy. Other students might be jealous of her power or popularity. So they plot against her and make it seem like she's done something wrong, which is a form of betrayal. Sometimes, it's the wizarding world's political powers that betray her. They might see her as a threat to their status quo and try to undermine her in devious ways, like framing her for crimes she didn't commit.
Well, perhaps in the fanfiction, it shows that Harry's parents made a deal with Voldemort before their deaths. They promised to hand Harry over in exchange for something, like power or protection for themselves. But then things went wrong and they ended up dying, still leaving Harry feeling betrayed as he discovers this truth later. It could also be that his parents were actually working against the Order of the Phoenix all along and Harry was just a pawn in their real plan.
Another plot could be that Harry, while living with the Weasleys, discovers a hidden family secret. This secret could be related to their magic that has been passed down through generations but was somehow lost or forgotten. Harry's presence might trigger the revelation of this secret, and it could lead to an adventure where they have to find the missing pieces of the family's magical heritage.
I'm not sure about the specific plot of this fanfiction as it sounds rather unorthodox. It could be a very dark or alternate - universe take on the Harry Potter world where Harry goes against the Weasleys for some extreme reason.