One interesting concept could be the exploration of Zim's character in a darker light. Maybe he's more menacing and his plans are even more devious. For example, his attempts to take over Earth could involve more cruel and calculated actions towards the humans.
One common theme is often the power struggle. The Tallest Dark Princess is usually a very powerful character, and in fanfiction, there can be a lot of back - and - forth about power dynamics with Invader Zim. Another theme is the exploration of the strange and otherworldly nature of the Invader Zim universe. Writers might use the character of the Tallest Dark Princess to delve deeper into the unique aspects of this universe.
Often, there's a theme of self - discovery. As Female Zim is a different take on the character, she might be on a journey to figure out who she is in this new form. Also, the theme of adaptation is common. Just like in the original where Zim has to adapt to Earth, Female Zim may have her own unique ways of adapting, whether it's to Earth's environment or to the reactions of the other characters around her. And there's also the theme of power. How does being female change Zim's perception and use of power? This is something that many fanfictions like to play with.
It depends on how you look at it. Some fans consider the comics canon because they continue and enrich the storylines from the show. However, others might have reservations based on personal interpretations.
Well, it's a bit hard to give an exact number. Different publishers and creators have come up with various Invader Zim comic offerings over the years. You might have to do some research to get a precise count.
The dark fanfiction may also explore themes that the original series only hinted at or avoided. Such as the true nature of the Irken Empire in a more sinister way. It might show how Zim's loyalty to his home planet is more complex and disturbing, while the original series focused more on his individual antics on Earth.