Another idea is that she is haunted by a special kind of ghost that has a connection to her past. The Ghostbusters have to not only deal with this unique ghost but also help her face her past traumas. This would make for a more emotional and complex fanfiction story.
In a fanfiction, Peter's sister might start as a skeptic. But after seeing the real deal with the Ghostbusters, she decides to join them in a more administrative role at first. However, as time goes on, she learns how to use the proton packs and becomes an essential part of the team, much to Peter's initial surprise.
A plot could be that the female Ghostbusters are sent to an old, abandoned amusement park. The ghosts there are the spirits of former employees and visitors who died in freak accidents. The Ghostbusters have to figure out how to calm the ghosts and send them to the other side without destroying the park, which has historical significance.
Some interesting Ghostbusters fanfiction concepts could be centered around the ghosts themselves. For instance, a story where a particular ghost has the ability to possess inanimate objects and uses this power to create chaos in the city. The Ghostbusters would then have to figure out how to stop it without causing too much destruction. Another concept could be a time - travel fanfiction where the Ghostbusters go back in time to prevent a major ghost - related disaster from ever happening. This could involve meeting their younger selves or influencing key events in the past related to the supernatural.
One possible fanfiction could be about a female Ghostbuster who has a unique power to communicate with ghosts on a deeper level. She uses this ability to not only bust ghosts but also to understand their motives and stories. For example, she might encounter a friendly ghost who was wrongly accused of being malicious and she tries to clear its name while still maintaining the balance between the living and the dead world.
One idea could be to explore the backstories of the Ghostbusters' equipment. For example, how Egon came up with the design for the proton packs. Another could be a story where the Ghostbusters have to deal with a powerful ghost from another dimension that has unique abilities they've never faced before. Maybe a story about the team's early days, when they were just starting out and trying to get their business off the ground.
Maybe an OC who is an international Ghostbuster, coming to the 2016 team with different techniques and cultural beliefs about ghosts. This OC could introduce new ways of dealing with ghosts that are based on ancient traditions from their home country, causing some interesting clashes and also new learning experiences for the whole team.
One idea could be a new type of ghost that is immune to the traditional proton packs, forcing the Ghostbusters to develop a new technology. Another could be a story where the Ghostbusters are transported to an alternate dimension full of super - powerful ghosts. Or perhaps a plot where a former Ghostbuster returns as a ghost himself, causing moral and practical dilemmas for the team.
Another plot could involve a crossover with 'Men in Black'. The two groups could initially be at odds as they deal with different types of 'paranormal' entities. But then they discover a common threat that is both extraterrestrial and ghost - like. They have to combine their resources, the Ghostbusters' knowledge of the spirit world and the Men in Black's expertise in dealing with aliens, to save the world from this new and dangerous entity.
A more character - driven plot for the fanfiction could be about one of the kids in Ghostbusters Afterlife struggling with the responsibility of being a Ghostbuster. They might feel like they're not living up to the legacy of their family. Through a series of events, they overcome their self - doubt and prove themselves to be a worthy part of the Ghostbusting team.
One idea could be that the twin sister also has spider - like abilities but uses them in a different way. Maybe she focuses more on using her powers for scientific research and discovery, while Peter is more into the superhero aspect. For example, she could be developing a new type of web fluid that has additional properties.