In some fanfiction, they could be on a quest to find a hidden magical artifact that was once owned by a great wizard. Along the way, they encounter various magical creatures and overcome obstacles using their combined skills and courage. Neville's knowledge of Herbology and Harry's combat skills would make them a great team. For example, Neville could use his knowledge of plants to create barriers or distractions while Harry battles any dark wizards or dangerous creatures that try to stop them.
In some fanfictions, their twin status might change the way the Sorting Hat sorts them. Instead of Harry going to Gryffindor, perhaps they both end up in Hufflepuff because of their shared values that are more in line with that house. This could lead to a completely different story arc where they are known for their loyalty and hard work rather than Harry's typical Gryffindor - like heroics. Also, their family relationships would be different. The Dursleys might have to deal with two magical children instead of one, which could change the way Harry (and Neville) grow up and view the Muggle world.
One possible plotline could be Harry and Neville teaming up to discover a new spell or magical ability that has been long forgotten in Hogwarts. They might explore the Forbidden Forest together in search of ingredients for a potion related to this discovery.
Luna Lovegood could also be an interesting addition. Her unique perspective on magic and the wizarding world might bring new ideas to the group. For instance, she could have insights about some of the more mysterious magical creatures or phenomena that they come across, which could be crucial in their quests or battles.
One interesting plotline could be Neville, who is already good at Herbology, discovers a new way to use plants in potions with Harry's help. This changes the way potions are made at Hogwarts.
Another interesting plot is when they are both part of a magical competition. They start as rivals but end up learning from each other. In one particular fanfiction, they are in a dueling tournament. Through the duels and the preparation for them, they see each other in a new light and form an unexpected bond.
Well, perhaps in the fanfiction, the pregnancy could be a result of some sort of magical accident. For example, a misfired spell that has unintended consequences. Then, Neville and fem Harry would have to deal with not only the physical changes but also the emotional turmoil. They might seek help from their friends like Hermione and Ron, who could offer different perspectives on how to handle this situation.
Well, one possible plotline could be Neville's hidden powers being explored even more deeply. Maybe he discovers a new spell or magical ability that helps him and his friends in a big way. Another could be Neville having a more central role in a mystery at Hogwarts, like uncovering a secret society or a long - lost magic item.
One interesting plotline could be Ash becoming a super powerful trainer overnight in the fanfiction. Maybe he discovers a new type of Pokemon power that gives him an edge in battles.
One plotline could be them teaming up to outwit the Slytherins in a series of magical challenges. They use their combined skills, Harry's courage and Neville's knowledge of plants, to create obstacles for the Slytherins in a magical maze competition.
One possible plotline could be Neville struggling to hide her true gender identity while dealing with the challenges at Hogwarts. Maybe she has to constantly come up with excuses for not participating in certain all - boy activities.