I understand that the specific story goal is shared by all the characters (e.g. to find the diamond), but is the requirement the same also, or are there variations on the requirement? similarly, the pre requisite as stated in the engine is one term, but i assume that that term is “clothed” differently from character to character, in a way that story goal is not.
I think you’re correct: the requirements can be anything, and there can be many requirements, as long as they’re necessary to achieve the Goal. I don’t think a single requirement has to be done by all the characters. In some stories, even the Antagonist might be tied to the Requirements and Prerequisites.
“Requirement” and “Prerequisite” are singular terms in the engine, but they (and a lot of other story points) can have numerous examples. I think part of the reason why is to avoid confusion between the Variation “Prerequisites” (under Learning) and the Additional Appreciation of “Prerequisite”.
I’d say there are some cases where while the Story Goal is shared by all characters, there might also be a “mini-Goal” alongside it that may not be (such as the Inigo Montoya substory in The Princess Bride).