Well, Wiz is really unique in the Konosuba light novel. She is extremely intelligent. Her knowledge about magic and the various creatures in the world is vast. This often comes in handy for the main characters. Also, she has a very kind heart for a lich. She runs a magic item shop and is always fair in her dealings, which is quite different from the typical portrayal of liches in other fantasies.
In 'The Wiz', the place is Oz, which is a fantastical land full of strange creatures and magical places. The time is not clearly defined in a historical or modern sense. It's more about the journey through this magical land where different events occur without being tied to a particular time like our normal world. For example, the characters experience various adventures and challenges in Oz that could happen at any time within this enchanted realm.
Well, considering the nature of many visual novels, a theme of self - discovery could be present. Kazuma and Wiz may learn more about themselves and their capabilities as they progress through the story. Also, a theme of good versus evil is a common one. They might be fighting against some sort of antagonist or trying to right a wrong in their world.
Well, it depends on the nature of the fanfic. If it adheres to ethical and respectful standards, not containing any offensive or inappropriate content, then it can be appropriate. Fanfic can be a creative way to explore characters and relationships in a new light.