Ludonarrative harmony
Also said as Ludonarrative resonance
The rules and the story say the same thing, so playing the game is itself the telling of the story.
When the rules carry the theme, the writing has less to do. Players feel the point in their hands and nobody has to explain it.
Say it
“Make death part of the fiction: the player wakes at the inn, the innkeeper mentions how they died, and each death moves one story beat forward instead of reloading.”
Where you’ve seen it
In Hades, Zagreus keeps trying to escape the underworld, and dying sends him back through the blood pool to the House of Hades, where characters talk about how the last attempt went. Failure is the plot.
Not to be confused with tutorial in the fiction
Dressing a button prompt up as a character speaking is only a coat of paint. Harmony means the rule itself means what the story means.