spin-off
Also known as sidequel, spinoff, gaiden, television spin-off, television spinoff, TV spin-off, TV spinoff, radio spin-off
narrative work derived from existing works
Article
Cover of the Adventures of Huckleberry Finn book, a spin-off of The Adventures of Tom Sawyer
A spinoff or spin-off is any narrative work derived from an already existing work that focuses on different aspects from the original work.