Perhaps a plot could revolve around Zim as a girl forming different relationships. For example, she might develop a unique friendship with Dib that is different from the typical male - Zim and Dib dynamic. Or she could have a female - centered friendship that helps her navigate the human world in a new way.
A possible plot could be that Zim, as a girl, discovers new aspects of her identity. She might start to question the Irken way of life more deeply. She could also be more in tune with emotions like empathy, which could lead her on a different path in her attempts to conquer Earth. Maybe she realizes that there are better ways to interact with the humans than just through invasion and destruction.
One possible plot idea could be that Eren has been hiding her gender to fit into the military or a male - dominated society. As the story progresses, her secret could be gradually revealed, causing shockwaves among her comrades. This could lead to some characters having to re - evaluate their relationships with her, and there could be both positive and negative reactions.
In this fanfic, Zim and Gaz could meet at the beach during a storm. Zim's ship malfunctions and he crashes near the beach. Gaz is taking shelter from the storm in a beach hut. They are forced to stay together until the storm passes. At first, there is a lot of tension and distrust. But as they share some of their snacks (Zim's Irken rations and Gaz's game - themed treats), they begin to open up and find that they have more in common than they thought, like their love for solitude in a way.
Here's a more detailed fanfiction idea. In a world where the Powerpuff Girls have been unable to stop a powerful new villain, they seek help from Dib, who then brings them to face Zim. Zim, thinking he can use this situation to his advantage, offers to help them. But in reality, he has his own plans to take over both Townsville and the Earth. As they work together, the Powerpuff Girls start to notice Zim's true intentions. Bubbles tries to befriend Gir to get more information, while Blossom tries to keep Zim in check. Buttercup is more skeptical and constantly on guard. Meanwhile, Dib is trying to document everything for his own records, hoping to finally prove Zim is an alien once and for all.
One idea could be a crossover with 'The Simpsons'. Zim could try to infiltrate Springfield, thinking it's a key Earth location for his invasion plans. Maybe he mistakes Homer for a powerful Earth leader and tries all sorts of wacky schemes to take over the town through him.
Another possibility is a fanfic set in an alternate universe where Gir and Zim are friends from the start. They go on adventures around the galaxy, with Gir's wacky antics often getting them into and out of trouble as they encounter different alien races and cultures.
Well, it could be about a space girl who encounters Invader Zim. Maybe she tries to stop his evil plans on Earth. She might use her special powers from outer space to outwit Zim and his various gadgets.
Perhaps there is some sort of magical or technological mishap. Let's say a device Zim was working on malfunctioned and affected Gaz in a way that made her pregnant. Gaz, being the tough one, is determined to figure out a solution on her own, but Zim, realizing the gravity of the situation, tries to make amends and help. They could go on a journey to find a way to reverse the process or come to terms with it and plan for the future together.
One popular Invader Zim girl fanfic might be those that focus on a female character's adventures in the strange world of Invader Zim. For example, a story where a girl discovers Zim's true identity and has to decide whether to expose him or help him in his bumbling attempts at world domination.
Perhaps Gaston, now a girl, falls in love with someone unexpected. As a male, he was always focused on Belle, but as a female, she realizes that there are other qualities she values in a partner. She might also face rejection from her former male friends who can't accept the change, which leads to a story about self - discovery and finding new friends who accept her for who she is now.
One plot idea could be a cooking competition where the main character has to make the best chowder and schnitzel. Another could be a story about a family that has a secret recipe for either chowder or schnitzel that they pass down through generations.