A great plot for 'the last great time war fanfic' would be to follow a character who has the power to manipulate time but is conflicted about which side to use it for. This character could be in a position where they see the good and bad in both sides of the war. As the story progresses, they might try to find a third way to end the war that doesn't involve complete destruction. They could encounter various challenges and moral dilemmas along the way as they interact with different factions in the time war.
One idea could be exploring the untold stories of the soldiers on the front lines. Maybe focus on a small group who are trying to complete a secret mission during the chaos of the time war. Another could be delving into the origin of the time war and how it could have been prevented from the perspective of a time - traveling historian.
One idea could be exploring the backstories of the minor characters in the War of the Last Alliance. Maybe there was a young soldier who had a secret love interest back home and his journey was not just about the war but also about getting back to her.
One idea could be exploring the origin of the Mushroom War in more detail. Maybe there are some hidden causes or events that led to it. Another could be focusing on the characters' lives before the war and how it changed them. For example, how Finn's family was affected.
One idea could be exploring the backstories of minor characters during the Great War. Maybe show how they got involved and what their personal stakes were.
You could write a fanfic about how the Mushroom War affected the magical elements in the Adventure Time world. Maybe the war disrupted the balance of magic, and certain characters are on a quest to restore it. They might encounter strange new magical creatures or phenomena that were born out of the chaos of the war.
One idea could be to focus on a young and unknown ninja who rises to prominence during the war. They might start with simple missions like scouting but gradually become crucial in major battles, perhaps by using a unique and unexpected jutsu.
One idea could be that the last dragon is discovered by a young adventurer. They form an unlikely bond and together they set out to find a way to save the dragon's kind from extinction. Maybe there are ancient prophecies or hidden magic involved.
One idea could be exploring an alternate timeline where Aang fails to defeat the Fire Lord. Maybe in this timeline, the Fire Nation completely takes over the world, and the remaining benders have to go into hiding and plan a long - term resistance. Another plot could be focusing on a new airbender discovered long after Aang's time, and their journey to master airbending without the guidance Aang had.
A cool plot for 'the last kingdom fanfic' might be to have a character be transported back in time to a crucial moment in the kingdom's history. They would have the knowledge of what's to come but struggle to convince others to believe them. This could lead to all sorts of interesting twists. Or you could write about a character who is secretly training a group of women to be warriors in a society that doesn't really accept that. It would be about breaking gender norms and the challenges they face in a war - torn world.
Well, in 'the last great time war fanfiction', the concept of alternate timelines is often fascinating. It could show how different decisions during the war led to various outcomes in different timelines. Some fanfictions might focus on the moral dilemmas of the war. Since time is involved, the idea of sacrificing one timeline to save another could be explored. And the technology used in the time war is also an interesting aspect. There could be new types of time - based weapons or defenses that are not in the original story, which can create exciting new plotlines.
One idea could be exploring the backstories of the characters during the Great War. For example, how Ruby's ancestors first discovered their powers and how they were used in the war.