In an 'advanced earth fanfiction', perhaps the Earth has mastered time travel. Scientists use this to correct historical mistakes, like preventing major environmental disasters. This would have a huge impact on the present day, with different species that were once endangered now thriving. There could also be a story about a group of people who discover a hidden, highly advanced civilization within the Earth's core that has been influencing human progress all along.
One interesting idea could be how the Dust in RWBY might have originated from certain minerals unique to Earth's history. Maybe in the fanfiction, Dust was a by - product of some ancient geological processes on Earth.
One idea could be exploring the backstories of the Taelons in more detail. Maybe a fanfiction about a Taelon who questions their race's motives and actions on Earth. Another could be a story focused on the human resistance, their daily struggles and how they plan their strategies. A third idea might be a love story between a human and a Taelon who try to bridge the gap between their two species.
One idea could be that Godzilla Earth teams up with a group of humans who have developed advanced technology to fight off an alien invasion. The humans initially fear Godzilla but soon realize they need his power.
A cool plot could involve a crossover with the 'Alien' franchise. The soldiers in Call of Duty Advanced Warfare could be sent to a distant planet where they encounter the deadly Xenomorphs. They would have to use their advanced military skills and weaponry to survive against these terrifying creatures. It could also be interesting if there was a crossover with a post - apocalyptic game like 'Fallout'. The Advanced Warfare characters could end up in the wastelands of 'Fallout', trying to adapt to the new environment and find a way back to their own world while dealing with the various threats in the Fallout universe.
One idea could be a crossover of characters from different Arrowverse shows on Earth X. For example, having Barry Allen from 'The Flash' team up with Kara Danvers from 'Supergirl' to fight against the evil regime on Earth X. They could use their super - speed and super - strength respectively to take on the powerful foes there.
Maybe there's a fanfiction where a Sith Lord tries to take over Earth. The Earth's military would be no match for the Sith's powers at first. But then, through some clever thinking and the discovery of a hidden Earth - based energy source similar to the Force, they start to fight back.
For 'a child of earth and sky fanfiction', a plot idea could be centered around the character's discovery of an ancient civilization that was closely tied to the earth and sky. They learn the secrets and wisdom of this civilization which gives them new abilities. They then use these abilities to face a natural disaster that threatens to destroy the balance between the earth and sky. Along the way, they form bonds with other characters who also have a connection to the earth and sky, and together they fight to preserve the world as they know it.
One idea could be a crossover where characters from Earth's history, like ancient Egyptian pharaohs, team up with Jedi from Star Wars to fight against the Goa'uld from Stargate. They could combine their unique powers and technologies. For example, the Jedi's use of the Force and lightsabers along with the pharaohs' knowledge of magic and the Goa'uld's advanced weaponry would make for an exciting story.
Perhaps in the fanfiction, the technology from Star Wars is used to explore the deepest parts of Planet Earth. For example, using starships to reach unexplored caves or the ocean floor.
A crossover with Stargate SG - 1 could also be fascinating. The Goa'uld and the Taelons both have an interest in power and domination. The SGC could get involved when they notice the Taelons' activities on Earth. They might try to figure out if the Taelons are another alien race like the Goa'uld or something entirely different.