One interesting plotline could be Hermione using her vast knowledge to solve a mystery that the teachers overlook. For example, she might discover a hidden clue about the Chamber of Secrets that leads Harry and her on a secret adventure within the school.
A possible plotline is that Harry and Hermione form an even closer bond during their second year. They could be working together to protect a new student who is being targeted by the heir of Slytherin. This would involve them using their magic skills in creative ways and relying on each other's strengths.
A possible plotline is that in their fourth year, there is a new student who seems to be a threat to Harry. Hermione suspects that this student has some connection to the Death Eaters. She and Harry start to investigate. Along the way, they face many challenges and misunderstandings. But through it all, they learn to trust each other more and their friendship blossoms into something more as they work to protect Hogwarts from this potential threat.
In some fanfictions, there could be a plotline where Harry and Hermione start to realize their feelings for each other in a different way during their 6th year. They've been through so much together, and this year could be the turning point where their relationship evolves from just friendship. They might have more private moments, sharing their fears and hopes, and this newfound closeness could lead to a whole new dynamic in their relationship.
Some fanfictions explore a different relationship dynamic between them. Maybe Harry has a problem that only Hermione can understand and help him with, and this brings them closer in a way that's different from their normal friendship. It could be something related to his connection with Voldemort or his family history.
In some fanfictions, their training might involve time - traveling. Maybe they go back in time to learn from the founders of Hogwarts. Harry could learn how to better control his connection to Voldemort through this time - traveling training, and Hermione could study ancient magic from the founders. This would add a whole new dimension to their skills and knowledge.
One possible plotline could be Hermione using her intelligence to create a stable and loving home environment for Harry. Maybe she helps him deal with his PTSD from his past traumas. Another could be them facing magical threats together as a family, with Hermione teaching Harry new spells and ways to protect himself.
One interesting plotline could be Harry and Hermione discovering a long - lost secret vault in Gringotts. Maybe it contains powerful magical artifacts that can change the course of the wizarding war. Another could be that they are on a mission to retrieve something from the vault that is crucial for their fight against Voldemort, like a spellbook with ancient and powerful spells.
One possible plotline could be that they are practicing magic for an upcoming difficult exam at Hogwarts. They might be working on advanced spells like the Patronus charm and Hermione is helping Harry perfect it.
One possible plotline could be that they escape from a dark wizard's lair. Maybe they use their combined magic skills and Hermione's extensive knowledge to find a secret passage out. Another could be escaping from a dangerous magical creature's territory by using clever spells and potions.
Perhaps a plot where they all become animagi and have to use their animal forms to solve a mystery in the Forbidden Forest. Draco as a sleek snake, Harry as a stag, and Hermione as an otter, they must navigate the forest's dangers and uncover the truth about a strange magical disturbance.
A plotline could involve the relationship between Harry, Hermione, and their friends in the context of having twins. Their friends like Ron and Ginny could be very involved in the twins' lives. Ron might be the fun uncle who always brings the kids interesting magical gadgets, and Ginny could be the aunt who teaches them Quidditch. Also, the twins' education at Hogwarts could be a major plotline. They might face different challenges compared to other students due to their parents' fame.