You could write a 'the dark crystal fanfiction' about a Skeksis who has a change of heart. Perhaps this Skeksis realizes the error of their ways after seeing the destruction they've caused. They then try to secretly help the Gelflings, all while hiding their new - found compassion from the other Skeksis. This would add an interesting layer of drama and conflict to the story.
A possible plot for Dark Crystal human fanfiction is a human scientist who is researching parallel universes and accidentally crosses over into the world of the Dark Crystal. This scientist then tries to study the unique ecosystem and magic of Thra. Along the way, they get involved in the political and social struggles of the Gelflings and Skeksis. They might try to use their scientific knowledge to find a way to stop the Skeksis' tyranny and help the Gelflings reclaim their rightful place in Thra.
One idea could be a crossover with 'The Lord of the Rings'. The Skeksis could be interested in the power of the One Ring and try to get it from Frodo. This would create an epic battle between the good forces of Middle - earth and the evil Skeksis. Another idea is a crossover with 'Star Wars'. The Gelfling could be like the Jedi, with their own special powers and connection to a kind of 'Force' in the Dark Crystal universe. They could team up with the Jedi to fight against a common enemy.
Another interesting fanfiction idea would be to have a character from The Dark Crystal, like Jen, end up at Hogwarts. Jen could learn about magic and how it differs from the magic in his own world. He might form friendships with the Hogwarts students and together they could face a common threat that somehow links the two universes, like a dark force that wants to take over both the wizarding world and the world of The Dark Crystal.
One idea could be exploring the backstory of a minor Gelfling character. Maybe they have a secret connection to the Skeksis that they're trying to hide. Another could be a story about Gelflings from different clans coming together to form an even stronger resistance before the events of the show. And a third could be a fanfiction where a Gelfling discovers a new power within themselves that could potentially turn the tide against the Skeksis.
One interesting concept could be the exploration of human - Dark Crystal world interactions. Maybe humans are trying to understand the unique magic or power systems in the Dark Crystal universe.
One idea could be a story about Kira's adventures in exploring new parts of the Dark Crystal world. She could discover hidden caves filled with ancient secrets or encounter new and strange creatures that she has to befriend or outwit.
One idea could be exploring an alternate timeline where the main character makes different choices in the game. For example, choosing a different starter Pokemon and how that changes their entire journey through the Johto region.
One idea could be Ash and Crystal teaming up to explore a new, mysterious region filled with rare Pokemon. They could encounter a powerful and previously unknown Legendary Pokemon that they have to work together to understand and protect.
One idea could be a story about a trainer who discovers a rare and powerful Pokemon in the Johto region that is not typically found in the games. For example, a shiny, alpha form of a Pokemon like Totodile. The trainer then has to protect this Pokemon from a mysterious organization that wants to use it for evil purposes.
One idea could be a crossover with the Harry Potter universe. Sailor Moon and her friends could attend Hogwarts and have to deal with both magical threats from the wizarding world and the dark forces they usually face. For example, they might help the students at Hogwarts fight off a new kind of dark magic that has similarities to the dark energy they combat in their own world.