One idea could be to explore the backstory of a minor character from the movie. For example, a young vampire who was turned during the wars but has unique powers. Another could be a love story between a vampire and a lycan that defies the age - old feud in the Underworld Blood Wars universe. Maybe they team up to stop a greater evil that neither side was aware of.
A great plot for an Underworld Blood Wars fanfic could be a time - travel story. A character goes back in time to before the blood wars started and tries to prevent it. This would involve changing the relationships between the vampires and lycans from the very beginning. They could introduce new technologies or alliances that would change the course of history in the Underworld.
One idea could be to explore the backstories of some of the minor characters in more depth. For example, a side character who has always been in the shadows could have a secret past that ties into the main conflict in a unique way.
One idea could be a crossover where characters from the Underworld and Divergent universes have to team up. For example, Selene from Underworld and Tris from Divergent might find themselves in a situation where they need to combine their skills to fight a common enemy. Maybe a new vampire - faction hybrid is created that threatens both of their worlds, and they have to figure out how to stop it.
Well, you could write a fanfic that focuses on the backstories of the characters in 'Blood of Olympus'. Maybe explore how Percy Jackson became the hero he is from a different perspective. Or create a plot where the gods interfere more directly in the demigods' quests in the fanfic. This could add more drama and tension as the demigods have to deal with the gods' complex personalities and motives on top of their existing challenges.
Perhaps a fanfic where Naruto's blood has some special connection to an ancient and powerful demon. The demon is slowly being awakened due to some dark magic related to Naruto's blood. Naruto has to face not only the threat of the demon but also the distrust from some in the village who think his blood is a danger. He must prove that he can control this situation and keep the village safe.
Another plot could focus on the origin stories of some of the side characters. For instance, the backstory of Yukina Himeragi. How did she become an attack mage? What kind of training did she go through? A fanfic could expand on this and also show how her past experiences influence her actions and relationships in the present story.
One idea could be exploring the backstories of the characters more deeply. Maybe delving into their childhoods and how those experiences shaped them into the people they are in the story. Another could be creating an alternate universe where the main characters have different occupations or abilities.
Selene is always an interesting character to focus on. Her strength and determination as a vampire make her a great protagonist. You can explore more of her past and her internal struggles during the blood wars. Another is David, with his complex relationship with Selene and his own ideas about the future of the vampire race.
The main plot involves intense vampire - lycan wars. There are power struggles among different vampire clans. Selene, the main character, is caught in the middle of these battles as she tries to protect her kind and uncover secrets that could change the balance of power forever.
One idea could be a story about a young demigod who discovers a hidden power within themself and has to use it to stop an ancient evil that is rising in the demigod world. This could involve a journey of self - discovery as well as battles against powerful foes.
One idea could be a story about an underdog character in the Echidna Wars who rises to become a great hero. Maybe they start off as a simple foot soldier but through their wits and determination, they turn the tide of a major battle.