One more plot could involve Ginny. What if Ginny was under the influence of a love potion given to her by someone who wants to use her to get to Harry? She might accidentally give away Harry's secrets or lead him into a trap. This would be a heartbreaking betrayal for Harry as he has a soft spot for Ginny.
A plot idea could be that Neville is forced by some dark magic to betray Harry. Neville has always been a bit of an outcast and maybe some dark wizard finds a way to use his insecurities against him. He could leak some of Harry's plans regarding the Triwizard Tournament tasks, which would put Harry in great danger.
One idea could be exploring a different version of the Triwizard Tournament. For example, what if there were more magical creatures involved in the tasks? Another could be focusing on Harry's relationship with Sirius during that year in a more in - depth way, like Sirius secretly guiding Harry through some of the tournament challenges. Maybe also a plot where a new student arrives who has a connection to Voldemort's past that no one is aware of and they try to disrupt the tournament.
Maybe in this fanfiction AU, the relationship between Harry and Hermione develops romantically during the fourth year. This would change the dynamics of their friendship and how they interact with Ron. They could face challenges together in the tournament, relying on their newfound feelings to get through difficult situations.
One idea could be that a character inherits a powerful but dark magical item which causes others to suspect betrayal. For example, if a minor character inherits a cursed object that was once used by a Death Eater, and suddenly people start to question their loyalty.
One possible betrayal in Harry Potter's fourth year could be when some students believed the false rumors about Harry being a cheater in the Triwizard Tournament. In fanfiction, this could be explored further. For example, Hermione might initially doubt Harry due to the overwhelming rumors, creating a sense of betrayal for Harry. However, as the story progresses, she realizes the truth and they reconcile.
One interesting idea could be a betrayal within the Order of the Phoenix. Maybe a member is secretly working for Voldemort and revealing the Order's plans. Another could be a betrayal among Hogwarts students, like a best friend turning on another due to jealousy over academic achievements or popularity. It could also be a teacher betraying Dumbledore's trust for personal gain or a darker ideology.
One plot idea could be Harry struggling with his newfound alcohol problem while also dealing with the Triwizard Tournament. Maybe his drinking starts as a way to cope with the stress and danger, but it quickly gets out of control and affects his performance in the tasks. Another could be his friends trying to stage an intervention, which causes a rift between them as Harry doesn't want to admit he has a problem.
Perhaps in the fanfiction, we could see a different side of the foreign students. Like, the Beauxbatons and Durmstrang students could have their own hidden agendas. One of them might be in love with Harry and tries to protect him during the tournament tasks. This would create a whole new dynamic of relationships and loyalties within the story.
Another interesting plot could be that Harry's connection to Voldemort causes some strange magical disruptions during the Triwizard Tournament. These disruptions seem like accidents at first, but Harry gradually realizes they are being caused by his own dark - side related powers that are being awakened in his fourth year.
One idea could be that Ginny starts to show her true magical potential during their fourth year. Maybe she discovers a new spell that helps Harry in a Triwizard Tournament task. Another plot could be that Harry and Ginny have to work together secretly on a project related to the tournament, and during this time, their feelings for each other start to grow more deeply.
Another plot could revolve around Harry's Occlumency lessons. In fanfiction, it could be that instead of just trying to block his mind from Voldemort, he actually manages to use Occlumency to his advantage. He could start to plant false thoughts in Voldemort's mind through their connection, leading Voldemort astray in his plans.