I nominated Star Wars: A New Hope as a safety fandom following the example that Iron Man 1 could be nominated as a safety fandom as the first in the series that can be consumed alone. A New Hope has a runtime of only two hours. What's more, A New Hope has a lore that exists standalone as explicitly contradicted by later movies: it's the only movie where Darth Vader and Anakin Skywalker are two separate people. The idea was to have a prompt explicitly asking for something set in this contradicted backstory, which would not require consuming any other part of the franchise.