One alternative topic could be the dark elf's unique weaponry. For example, their use of poisoned daggers or enchanted bows. These weapons are often crafted with great skill and are an important part of their combat abilities.
The Dark Souls lore is centered around the cycle of the First Flame. It's about the struggle between light and dark. The undead are key as they are linked to the fading of the Flame. There are places like the Undead Asylum where your journey begins. It shows the desolation and the harsh reality of being undead.
The dark elf may be lonely. Living in a world separate from humans, she sees the man as an interesting specimen. Capturing him gives her the chance to interact with someone different, to learn about a new culture and way of life, even if her methods are rather extreme.
It's a bit of a gray area. The base lore of Dark Souls is not fanfiction as it's the foundation laid by the developers. However, the way fans expand on it, fill in the gaps, and create their own interpretations can be seen as fanfiction - like. For instance, the nature of the Abyss in Dark Souls has some official details, but fans have created elaborate theories about its origin and how it relates to other elements in the game, which is like fanfiction built on the existing lore.
The lore of Dark Souls has a lot to do with the cycle of fire and dark. The First Flame is central. When it was discovered, it changed the world. Souls were born from it. There are different regions in the game, each with its own backstory related to this overarching theme. For example, Lordran has a history tied to Gwyn and his actions.
This kind of novel plot is more common. You can refer to the following similar novels:
Lord of the Dark Forest: The elf who transmigrated into the novel has the genes of a dark elf and a nature elf, so he has unique abilities and characteristics. The relationship between the Dark Elves was a complicated triangle.
A dark elf teen usually has pale skin, which is almost like moonlight in the dark forest. Their hair is often black as the night sky, and it can be long and flowing or short and spiky. Their eyes are a distinct shade of purple or deep blue, like the rarest of jewels. They are slender in build, with a grace that comes from living among the trees and shadows.