The Demon Lord’s Castle Clerk

Fatalia is a transmigrator, a young white-haired succubus, and a poor child who somehow ended up in the Great Wilderness. In her mind, she also has a useless System that can only show her status screens. But one day, she successfully discovered another use for this useless System. Facing an abyss where you could receive rewards by paying a price, she said, "I want to sacrifice the System." And she succeeded. (This is a serious story about a succubus helping the Demon King turn the whole world upside down.) (One more reminder up front: the protagonist will grow up. For her mature appearance, refer to the cover. She won't stay a little girl forever.)