A really interesting plot could be a group of Space Marines who have been captured by the Borg. Instead of being assimilated immediately, they are used in some sort of experiment. One of the Marines manages to break free and starts to sabotage the Borg from within. He then has to find a way to communicate with the rest of his comrades outside and work together to defeat the Borg.
On the Borg side, the Borg Queen is often a central character. She is the one who commands the Borg collective and devises the plans to assimilate the Space Marines. For the Space Marines, you might have a tough and experienced sergeant. He is the leader who has to make difficult decisions during the battles against the Borg.
A fan fiction could also explore a parallel universe where Anakin and Darth Vader are two separate entities that co - exist. They are forced to fight not because of Anakin's fall, but due to some external force that wants to see the two most powerful Sith - like beings battle it out. This could lead to an exploration of their different fighting styles and the power dynamics between them.
Perhaps a fan fiction where the Yamato is suddenly invaded by a group of shape - shifting aliens. These aliens can take on the form of the crew members, causing chaos and paranoia on the ship as no one knows who is real and who is an impostor. The remaining real crew has to find a way to identify and defeat these aliens.
One idea could be to create a story where the characters from Office Space start a new business together outside of Initech. They could face new challenges and use their unique skills in different ways. For example, Peter could use his newfound confidence to lead the team in a more ethical and productive direction.
One idea could be to focus on the origin stories of the marines in the fanfic universe. Maybe explore how they were recruited and what their initial training was like.
One idea could be a story where the Mandalorian has to team up with an old enemy to fight a new, greater threat. Maybe a powerful Sith Lord emerges and they have to put aside their differences.
One idea could be exploring a different origin for Toothless. Maybe he was part of an ancient dragon tribe that was thought to be extinct. Another could be a story where Hiccup discovers a new dragon species that has unique abilities and forms an alliance with them. A third idea is a time - travel fan fiction where Hiccup goes back in time to prevent a great dragon war from ever starting.
A great plot for Warframe fan fiction could be a Tenno getting trapped in a parallel dimension where the rules of the Origin System are all messed up. They have to find a way back while dealing with strange versions of familiar enemies. Or perhaps a story about a Tenno who discovers a hidden Orokin vault that contains not only powerful weapons but also a secret that could change the balance of power in the Origin System. Also, a plot about a Tenno's struggle to control a newly acquired and extremely powerful Warframe that has a mind of its own could be really engaging.
Well, you could have a survivor fan fiction where a contestant has a hidden skill, like being able to communicate with animals on the island. This could give them an edge in finding food and avoiding danger. Or perhaps a story where there's a traitor within the group, someone who is secretly working with the show's producers to create more drama. Also, a plot where the survivors find a map that leads to a hidden part of the island with a bountiful supply of food and shelter.
One idea could be that the Ghostbusters discover a new type of ghost that can possess technology. So they have to find a way to stop it from taking over all the electronics in the city. It would be a race against time as the city starts to descend into chaos with machines going haywire.