Web fiction
Spin-off
A narrative work derived from an existing work that focuses on different aspects: a new vehicle for a side character, setting or premise.
A spin-off is "any narrative work derived from an already existing work that focuses on different aspects from the original work," and the label covers books, comics, radio, television, film, animation and games. The first modern media use is traced to 1941, when a supporting character left the radio show Fibber McGee and Molly to star in The Great Gildersleeve, starting "a trend known as the series spinoff." Adventures of Huckleberry Finn is the article's literary example, a spin-off from The Adventures of Tom Sawyer, and franchise television has produced spin-offs of spin-offs. Japanese has a word for the same move, gaiden, "side story," and a "sidequel" runs in the same timeframe as the original.
For novelists and serial writers a spin-off is leverage on work already done: a character or corner of the world that proved it holds an audience gets its own line. The risks are the ones a crossover shares, imported canon and clashing rules, and the management problem is the same as how to write a series: keep the shared facts straight.