One interesting plotline could be exploring Dumbledore's younger years through Harry's eyes. Maybe Harry discovers some old memories of Dumbledore's adventures as a young wizard, and it helps him understand Dumbledore better. This could also show how Dumbledore's past experiences shaped his decisions in dealing with Harry and the fight against Voldemort.
One interesting plotline could be how Dumbledore helps Harry discover his true magical potential beyond what he learned at Hogwarts. For example, he might introduce Harry to ancient and rare magic that was long forgotten. Another could be Harry's relationship with the wizarding community changing as he is now seen as Dumbledore's adopted son. This could lead to new friendships and alliances. Also, Dumbledore might train Harry to become a great leader in the wizarding world, preparing him for future threats that are much larger than Voldemort.
One interesting plotline could be exploring Dumbledore's family history in more depth through Harry's perspective. For example, how Dumbledore's past actions and family relationships might influence Harry's journey. Another could be a story where Harry discovers a long - lost relative who was also connected to Dumbledore's family. This could add a whole new dimension to the wizarding world he thought he knew.
One interesting plotline could be Harry learning advanced magic from Dumbledore that is not taught in the regular Hogwarts curriculum. For example, he might learn ancient spells for protection or divination techniques that are long forgotten.
In some fanfictions, Harry as Dumbledore's apprentice might have to deal with a dark prophecy that only he, with Dumbledore's guidance, can solve. This could lead to a journey where he has to make difficult choices between different paths, each with its own consequences for the wizarding community. It would be a great exploration of Harry's character growth and his relationship with Dumbledore in a more in - depth and unique context.
One interesting plotline could be a magical duel between them where they both use unique spells not seen in the original books. Maybe Dumbledore is under the influence of a dark spell, and Harry has to fight him to break the curse.
One interesting plotline could be exploring their early days at Hogwarts together. Maybe they were both brilliant students with different outlooks that gradually diverged. Another could be a story where they meet again after Dumbledore defeats Grindelwald, and there are still unresolved feelings and thoughts between them. A third one might be a fanfiction that delves into an alternate universe where they actually work together to achieve some 'greater good' that they both misinterpreted in different ways.
One possible plotline could be Dumbledore being judged for his actions regarding Harry Potter. For example, some fans might write about how his decisions to keep certain secrets from Harry were either right or wrong. Another could be his past associations being put under the microscope, like his relationship with Grindelwald.
In some fanfics, Dumbledore's Army could be involved in secret missions outside of Hogwarts. For example, they might go on a quest to find a hidden magical artifact that could help in the fight against Voldemort. This would add an element of adventure and mystery to the story.
A lot of fanfictions focus on the relationship between Harry and Dumbledore in a more emotional way. For example, a story could be about Harry having a hard time after Sirius's death and Dumbledore being there for him in a more fatherly way than in the original books. This could include Dumbledore sharing his own experiences of loss with Harry and helping him through the difficult time.
Perhaps Dumbledore is shown to have a secret alliance with Voldemort in the fanfiction. Harry stumbles upon evidence of this and is filled with rage and hatred. Or maybe Dumbledore had been manipulating Harry's emotions and actions from the very beginning to fit his own plans for the wizarding world, and once Harry realizes this, his hatred for Dumbledore grows. It could also be that Dumbledore has been hiding a powerful magical artifact that could have saved many lives but didn't, and Harry blames him for it.