Sacrifice, and Narrative Conflict
Sacrifice is a universal RPG system, though only technically. In practice, Sacrifice is a deconstruction of the entire RPG medium and dramatic storytelling.
There is, in fact, only one simple set of rules: your character can do anything that the narrative has established your character can do. When they want to do something that the narrative hasn’t established they can do, then they roll 2d6. If they roll a 12, then they succeed. If they don’t, they fail… unless they sacrifice something.