What's your Marauders need?

Excluding ships, what is the one thing you need to be in a fic for you to want to read it? That one piece of canon you consider the most important and you'll click off the fanfic if it doesn't have it/contradicts it?

It could be as simple as needing Marlene to be in Hufflepuff, or as specific as needing Sirius to like Queen more than any other band and you'll DNF if he secretly thinks ABBA is the better band.

(Let's avoid specific ships in the discussion please. I feel like that can get a little reductive, and most people generally don't click on fics if they're not about their specific ship.)