When you are choosing names for a fantasy world of your own creation, you can decide what kind of names this foreign world has: Completely invented names, slightly altered names, exotic names, or just slightly unusual names. (I would not recommend anyone use Ashley and Aiden names for their fantasy characters).
Completely invented names are very difficult to create (once you Yahoo! Search for a name you’ve created, you’ll often find it already exists if only as a chat room handle), and nearly impossible to sustain consistently for all the characters of a given world. Slightly altered names can be hard, but if you base them completely on one culture (e.g. Welsh) you have consistency already built in. Exotic names or slightly unusual names (like Katniss and Primrose from the Hunger Games) are a good choice, if only because they will sound and read as more natural than many invented names.
No matter what type of names you chose for your fantasy world, however, I urge you to be consistent in the naming style of people within a culture in that world. This can be hard work, but it also can infuse your fantasy writing with the realism and believability that will allow readers to immerse themselves completely into the world of your creation.
Just remember, no matter how difficult this may seem to you, outside namers, like myself, have it even harder.
When I was asked to name fantasy characters (which was often), I didn’t have the luxury to create a naming style for a novel world: I had to decipher what naming style the writer was unconsciously creating and then try to mimic it.
In the Character of the Week example from this past Monday, I was given only three names from the novel: Colum, a character from our world; Omena, a seer; and Arianna. Eliminating the character from our world, I had one very exotic name and one very typical name: Not the best combination to decipher a naming style.
The best I could do in this situation is to assume that the writer meant to choose an unusual name for Arianna, and unconsciously chose one of the top 400 female names of the character’s birth year (in the USA, on Earth). I usually do not offer unsolicited advice to writers who ask me for names (I sometimes do, but not usually). In this case, I almost wish I had.
If I had nosed in with my two bits, I would have told the writer that he should go with a more consistent naming style for the seer, the girl, and the other characters on their world, perhaps names based on Finnish (one option for the ethnographic history of Omena). And if I had suggested a change like that, I would have suggested that the girl’s “real name” should be something like Elina or Kaisa, and the name the boy gives to her could be something like Arianna.
Creating a consistent naming style is just one part of world-building, and I would argue that it is an important one. The characters’ names give a flavor to the world that is ever present every time Kaisa says something, or Arianna flips her hair, or Aurora looks at Colum, or Elina cries out in anger and frustration. No matter what they are doing, their names are always there to help the readers peer into the fantasy world of your creation.