A really interesting plot could be that Ariana's spirit is trapped in a limbo of sorts. Harry, with his penchant for getting into extraordinary situations, discovers a way to communicate with her. They then work together to free her spirit. Along the way, Harry learns more about Dumbledore's past through Ariana's memories, which in turn helps him in his own battles against the remaining dark forces in the wizarding world.
Well, some fanfictions might focus on Ariana's magic. Since her magic was unstable, a story could revolve around her learning to control it in a different way than what Albus and Aberforth thought was best. This could lead to a split in their family not just because of the incident with the Muggle boys but also due to differences in how to handle Ariana's powers. Or, there could be a time - travel based fanfic where a character from the future tries to save Ariana from her tragic fate, changing the course of the Dumbledore family history.
One idea could be Dumbledore misplacing his memories and the students of Hogwarts having to help him retrieve them. It could lead to a series of adventures where they discover secrets about Dumbledore's past that were long forgotten.
A possible plot idea is that the duel is a miscommunication. Dumbledore thinks Harry has been influenced by dark magic, and Harry thinks Dumbledore has turned against him. As they duel, they gradually realize the misunderstanding and work together to find the real source of the problem. Or perhaps it's a time - traveling duel where future - Harry has to duel past - Dumbledore to prevent a dark future.
She is often portrayed as a tragic figure. Writers usually emphasize her delicate state, both physically and mentally. Her magic is also a key aspect in many portrayals, with it being either a source of her pain or a hidden power waiting to be unleashed.
One idea could be exploring Dumbledore's early years as a student. Maybe he had a secret friendship or rivalry that shaped his views. Another could be a story where Dumbledore has to face a powerful dark wizard before Voldemort, and how that experience influenced his later actions against the Dark Lord. A third idea is to write about Dumbledore's travels and the magical creatures and cultures he encountered during them, which might have given him insights for Hogwarts' teachings.
Perhaps Harry discovers a hidden room in Hogwarts that was Ariana's. As he explores it, he starts to feel a strange bond with her. He then uses magic to try and bring out her memories or essence. As he gets to know more about her, he starts to see her as a friend and someone he wants to protect, much like he does with his own friends.
In such a fanfiction, perhaps a major plot point is how Dumbledore trains Harry to face a new and greater threat. It could be a dark wizard more powerful than Voldemort, and Harry has to learn a whole new set of strategies and magic under Dumbledore's guidance. Harry might also develop a deeper understanding of the wizarding world's history and secrets through Dumbledore's teachings, which could be a key part of the plot.
Well, in some fanfictions, Ariana Grande might be a witch who uses her music to fight dark magic. For example, she could team up with Harry Potter to defeat a new dark wizard. Her songs could be turned into spells. Or perhaps she is a long - lost relative of a Hogwarts founder and she discovers her heritage while also dealing with her muggle - like fame in the wizarding world.
A great plot for a Potter Manor fanfiction could involve a mystery that surrounds the manor. For instance, strange noises at night lead Harry to uncover a long - forgotten chamber. It could also be about Harry restoring the manor to its former glory, perhaps with the help of Hermione's research on ancient magic used in the construction of such manors.
One idea could be that Ariana and Ethan team up to rescue a rare and powerful Pokemon that's being held captive by an evil organization. They start off distrusting each other but as they face challenges during the rescue, they learn to rely on one another.