So this is clearly going to require a bit more explanation as this will encompass many different universes (when I get to making them that is). Everything below this will be a setting inside of a universe because I've decided that it would just be easier to introduce a setting rather than one individual character. I feel as though a single character limits the amount you can do and the story you can tell as if it's only two characters interacting that's bound to get a bit boring. For any chapters below introduce whatever characters you'd like, if and only if, they fit into the setting. This includes being historically accurate to the time period, I don't care if it's incredibly accurate, for example if it's the 1940s and a character is a little 💅, they are probably going to be a bit more reserved. (cough cough foreshadowing the next chapter).
Anyways, I should warn you now that I will not be light on the scenarios. If you want to make one up then I would prefer to discuss it first, but other than that go crazy. All my prior rules still apply to these too.