There is this a class of fiction called “FanFic.” It can be good, it can be bad, it can be awful. The concept is that you take your favorite TV or Movie characters and write a story about them.
I believe it was Alan Dean Foster that wrote a bunch of Star Wars novels. James Blish wrote Star Trek novels. These novels extended the universe for these characters.
There are lots of stories written by random fans about their favorite characters. Just be careful if you go looking because you will find every type of story imaginable. Many of them Pornagraphic. If you have a favorite TV or Movie character it is almost a certainty that somebody has written a story about them doing the dirty in the dirtiest possible way with all sorts of different characters.
In the same way there are singer/songwriters that write and perform songs about their favorite TV or Movie characters. This is called “Filk” A play on the word “folk”.
In addition there are a number of songs that are written and performed at Ren Faires and SCA events which are modern takes done in older styles.
Note, this group has lots of NSFW songs.
This is a Ren song. If you are part of the cast and make it to the after hours party this is the sort of song you might here.
Hope you all enjoy.
Postscript: There is a song done to “Roll The Chariot” or “Drop of Nelson’s Blood” set in the Firefly Universe. If you happen to know the title or have a link, please let me know.