Essentially, this is when a Spin-Off of some kind (be it a sister show, reimagining, Gaiden Game, or what have you) is significantly darker than its main series counterpart(s).

There are several reasons for why this is done. One is the fact that spin-offs aren't marketed as heavily as main-series works, so most people who buy them are already fans of said work; as a result, creators can make much more adult-oriented works to pander to teenage and adult fans (who make up the majority of most fanbases). Another is to hit multiple demographics at once: younger kids will watch the main series, and as they grow older, they move on to the darker spin-off. Finally, spin-off material is often made by a different person or company, and if said person or company's