A more emotional fanfiction could focus on the relationship between the Fire Keeper and the Ashen One. What if the Fire Keeper develops feelings for the Ashen One that are more than just her duty - bound connection? This could lead to a complex and interesting story, with her having to balance her emotions with her important role.
One plot idea could be the Fire Keeper's journey to discover her true origin. Maybe she starts having strange dreams that lead her to explore forgotten areas of the game's world. Another could be a love story between the Fire Keeper and an unnamed warrior. They meet during the warrior's journey to link the fire and gradually fall in love, but their love is tested by the harsh realities of the Dark Souls universe. A third idea is that the Fire Keeper gains the ability to see the future and tries to change the fate of the world, which goes against the natural order of things in Dark Souls 3.
One plot idea could be that the Fire Keeper from Dark Souls is transported to another world in the crossover. There, she has to adapt to new rules and powers. Maybe she meets characters from the other universe who initially mistake her for something else due to her unique appearance and abilities from Dark Souls. Another idea is that she teams up with a character from the crossover world to fight a common enemy that threatens both of their realms. This enemy could be a powerful being that feeds on the essence of different worlds, and their combined knowledge and skills are the only hope to stop it.
Some 'Dark Souls Fire Keeper' fanfictions are about her role in a different timeline. What if the events in the game happened differently? Maybe she becomes a more active fighter instead of just a keeper. There could also be a fanfiction that delves into her dreams and visions. Since she has a connection to the First Flame, she might have prophetic dreams that could lead to new adventures or revelations. Additionally, a fanfiction could explore how she copes with the loneliness of her role and the constant cycle of death and rebirth in the Dark Souls universe.
The Ashen One is an obvious choice. Their connection in the game can be explored further in a fanfiction. They have a relationship based on the goal of the Ashen One's journey and the Fire Keeper's role. Another good character to pair with her could be the Emerald Herald. They both have a somewhat otherworldly quality and their interactions could bring out new aspects of the story. Also, the Siegward of Catarina could be interesting. His chivalrous nature could contrast with the Fire Keeper's more mysterious and ethereal presence, creating some great character dynamics.
One idea could be exploring the origin of the Age of Fire from the perspective of an unknown character. Maybe a commoner who witnesses the first spark of the Age of Fire and their journey to understand its significance.
To develop the Fire Keeper's character, you could start by exploring her backstory more deeply. Maybe in the crossover, she has flashbacks to her life before becoming a Fire Keeper. This could add more layers to her personality. Another way is to put her in situations that force her to change. For example, if she has to deal with a new type of magic in the crossover world, she might have to learn to adapt and grow in her understanding of magic.
Show her interactions with other characters in a way that is consistent with the game's lore. For instance, her conversations with the other inhabitants of Firelink Shrine can reveal a lot about her personality. If she is respectful but firm with the Handmaid, it shows her position of authority and her sense of propriety. Also, don't forget to include her connection to the First Flame, as it is a crucial part of her identity in the game.
One idea could be a crossover with 'The Lord of the Rings'. Picture the Dark Souls characters in Middle - earth, facing off against orcs and other dark creatures. Another could be a crossover with 'Bloodborne'. The gothic and nightmarish settings of both could blend well, with hunters and Dark Souls' warriors teaming up against a greater evil. A third idea might be a crossover with 'Final Fantasy'. The different magic systems and character classes could create really unique and exciting storylines.
A crossover with 'Final Fantasy' would be cool. The magic systems in both could be combined in interesting ways. For example, a Dark Souls 2 mage could learn some spells from a Final Fantasy character. Also, a crossover with 'The Elder Scrolls' series. The vast open worlds of both could create an amazing setting for the fanfiction. The character could explore different regions of Tamriel and use their Dark Souls 2 abilities to survive.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a large collection of fan - created works, and you can search specifically for 'Dark Souls Fire Keeper' fanfictions. Another option is FanFiction.net. There are many talented writers on there who might have written some great stories about the Fire Keeper.