Narrative design
Also said as Narrative designer, Game writing (the neighbouring job)
Deciding how the story works as a game: what the player learns when, what a choice can change, which systems carry which beats. Game writing is producing the words themselves.
Studios that treat these as one job tend to hire a writer too late and hand them a finished game with gaps in it. The structure is what decides whether any of the good lines can land.
Say it
“We need narrative design before we hire a writer: a list of every flag, what each quest can change, and where the player can walk off in the middle of a line.”
Where you’ve seen it
Inkle's 80 Days was written by Meg Jayanth, on top of the studio's own scripting language. The words and the machine deciding which words you see are two separate pieces of work.
Not to be confused with game writing
The writer decides what the character says. The narrative designer decides that a character should speak here, what triggers it, and what happens if the player has already walked off. Small teams have one person do both.