I would decide on an overall theme or skin for the session first.
This will determine how things in the story will appear.
Since your idea takes place inside the faerie realm I would assume that the player character is unable to perceive things for what they truly are. Instead everything takes on a symbolic appearance.
An example could be roman gods or greek myth, hermetic history, the characters life story or anything that suits your fancy. Whatever you chose make sure that everything in the story fits within the appearance of that theme.
Lets say you pick roman gods/mythology. Then you needs to pick roles for the characters and locations that appear.
It is a bit hard for me to come up with more concrete advice without more detailed knowledge of what you want to do with the plot specifically.
I can give you a parallel example of a plot I set in the magic realm. The plot had 2 stages as the players were trying to find the microcosm of one characters mind in order to kill part of his identity.
The first stage I called "the perpetual hotel". This place was essentially a trap created by the characters subconcious desire to not have part of his identity killed. The name "the perpetual hotel" is just a name I gave it to explain to myself the purpose and nature of the place. the players would get a more misleading name given to them. The way it worked is that the players would meet a guide there who would try to distract them by showing them endless rooms containing scenes depicting ways in which the offending piece of identity had helped them.
The second stage I called the "the high city". That place you could only reach by realizing that the "perpetual hotel" was a trap and in the process overcoming the relevant characters desire to preserve his identity.
Since the character was into norse mythology I decided that it would take on the appearance of valhalla and that the guide character would be Odin. Note that the guide wasnt actually Odin, it merely appeared that way. The way to get on was to simply demand of Odin that he show them the true way and he would do so. (I decided that Odin could not disobey a direct order since he was a representation of the characters mind and could not disobey the character). Since the plot was about the character doubting the value of magic all the scenes that odin would demonstrate related to how great magic is.
In the high city every piece of personality would be either a person there or a house or some other thing you might find in a city. Here the challenge was to find the proper person/structure without fucking around with anything else, since doing so might have unintended consequences. e.g. if they killed a person that represents the characters loyalty the character whose mind they were inside would wake up without a sense of loyalty.
Done right plots like this can be really great because you get to explore a world of symbols where everything makes sense differently.
I hope this helps with inspiration. If you share some more details about your aims for the plot and the character to experience it, I will be happy to help more.