Designing Situations for Story Games
Alex talks about designing scenarios for narrative games while keeping the spirit of "story now".
One thing you might not know about me is that my first two games in the TTRPG space were Advanced Dungeons and Dragons (2nd edition) almost immediately followed by Vampire: the Masquerade several years later. I loved AD&D, even though I didn't have too much opportunity to play it. So much, in fact, that I once grabbed my core three books and kept them with me as an EF-5 tornado passed overhead. Yeah, that really happened. (The house was fine, fortunately, and so were the AD&D books).
All that to say, my first introductions to the hobby were pretty firmly in the more traditional RPGs of the era. It took a while for me to "click" with how games like Apocalypse World and its many derivatives want to be played.
Once it did, though, I haven't really looked back. The "Story Game" branch of games has become one of my favorite kinds of games to play during TTRPG time. They're not the only games I play, or think about, but when given the choice I'll usually pick a story game (Powered by the Apocalypse or Forged in the Dark most often).
This isn't your typical adventure design

Mostly, story games are designed (whether explicitly or implicitly) for the players and GM to create a story in the moment, as you are playing. Contrast this to a lot of the modules and advice given in Pathfinder Adventure Paths and D&D core books from 3.5 onward, which have a set plot that it expects you to experience as a story.
I think this is why you do not see a lot of "adventures" in the "traditional" sense of them for PbtA or FitD games. It just doesn't work well when the action is driven by the characters, their motivations, and their flaws. Usually what you get is something like Monster of the Week: Codex of Worlds (affiliate link), where the setting is expanded and you get additional threats / starter "fronts" (which may not be called that) / other loose ideas for you to put together.
What, then, are you - the GM, expected to do?
Give them a lot of things they can hook onto in the fiction and let them choose what things they choose to pursue! Keep it dynamic, the world still moves along with the PCs, but their actions should have a direct impact on what's happening in the ongoing narrative.
Using Factions and Fronts
Factions and Fronts are present in a bunch of games with varying names (though faction is a pretty self-explanatory term in context), but for the following examples I'm going to draw on Dungeon World a fair amount, because they explain them well and there's a whole community guide on how to use them (among other great advice on how PbtA as a whole works).
Factions

"Factions" in PbtA games are pretty similar to the dictionary definition of faction - a group of people with an aligned agenda. Blades in the Dark gives you a whole pile of them to start with in the setting and during character creation the group's crew will have gained positive or negative reputation with those factions.
This is a great way to drive conflict in the game, positively aligned factions are liable to ask for help. Negatively aligned factions will likewise attempt to hinder the PCs activities.
Each of these factions will also have their own agenda that they're pursuing in the narrative, which will continue whether or not the players engage with them (or you drop it, depending on where the group wants to go with the fiction).
This is where fronts come in.
Fronts
The Dungeon World SRD has a full page on how fronts are designed, but I think the community guide does a better job of giving concrete examples. But, at their core, they are simply multi-stage processes for what a faction (or other entity) is currently planning and the steps that will occur for them to get there.
As the characters interact with the various fronts, they will either derail, ignore, or otherwise accelerate those fronts. The group has some leeway here, if you design too many fronts and the players aren't engaged with them, you can absolutely ignore them.
Fronts tend to be multi-faceted, and have multiple factions involved in them. Usually those factions will also be opposed to one another, creating conflict for the PCs to get embroiled in.
Let's have a look at the example front from the Dungeon World SRD, step by step.
An Example Front: The Opening of the White Gate
In this front, the game presents essentially a three-step process for the White Gate opening, and the events leading up to it.
Description and Cast
An ancient gate, buried for aeons in the icy north. It opens into a realm of pure light, guarded by the Argent Seraphim. It was crafted only to be opened at Judgment Day, so that the Seraphim could come forth and purge the realm of men. It was recently uncovered by the College of Arcanists, who do not yet understand its terrible power.
Oren Balserus, Arcanist Supreme
Hali’el, voice of the Seraphim
Drudge, a manservant
So we've got a gate, two factions, and the Gate itself. The factions do not appear together until the third phase of the action, and will likely be opposed to one another when that happens. Assuming the Arcanists want to shut the gate once they realize what they've done.
The action starts with this Danger:
The College of Arcanists (Cabal)
Impulse: to absorb those in power, to grow
Grim Portents
* The College sends an expedition to the Gate
* The Key is discovered
* The Gate’s Power is harnessed
* The College seizes control
Impending Doom: Usurpation
The Arcanists are going to do those bullet points in order, and if they're not stopped, the doom will come to pass. I actually think you can largely ignore the doom in linear fronts like this one. The "bad stuff" is pretty self evident as it progresses to the next phase.
At any point before the "College Seizes Control" phase, the PCs could derail their plans, if they are so inclined. In this example, the PCs might even be aligned to the College of Arcanists and want to help them research the gate. The main trick here is that these are the logical steps towards the threat.
Once they've seized control, they're going to try and open the thing.
The White Gate (Dark Portal)
Impulse: to disgorge demons
Grim Portents
The First Trumpet sounds
The Second Trumpet sounds
The Gate is opened
Impending Doom: Destruction
The gate here will sound two trumpets before it's opened. Until it opens up the PCs can attempt to stop the process. How that occurs is purposely left open-ended. Perhaps you introduce a moral dilemma: The gate's opening can only be closed by an offering of blood... all of the Arcanists should do. Alternatively, it could require a special macguffin that is far away, and you're now on a timer.
If you do nothing, the gate opens, and the Seraphim (the second faction) come pouring out.
The Argent Seraphim (Choir of Angels)
Impulse: to pass judgment
Grim Portents
A Champion is chosen
An organization of power is formed or co-opted
The Herald appears
Judgment is passed
Impending Doom: Tyranny
They're ready to wipe people from the face of the planet, but they're going to be fair about it by forcing you to choose a champion! This will likely be one of the PCs.
And anyhow, things spiral from there.
Actually Running Fronts
There are a couple of things I want to call out about running fronts like this:
- The more of them you're running at once, the more there is for you to keep track of. Dungeon World suggests you only run two at once, but depending on the group and your willingness to let stuff drop, I've had 4-5 different semi-connected things running at once.
- The example given is super linear and doesn't have faction interference, and I enjoy having more than one faction react to the same ongoing threat. For example, I like to have factions aligned with each other on certain things and opposed on others.
- It's okay to let fronts die if the players never engage with a threat. That's just them expressing the things they're interested in. They should be the main drivers of the narrative.
What's cool about all of this is you can align the fronts to the factions which the players are most aligned with, or use it as a vehicle to introduce new factions. The PCs are going to be forces of their own throughout the story.
Wrap Up
The tl;dr here is ideally you don't build out a full "traditional" adventure in narrative games, instead you have the drivers pressure the PCs and generate the ongoing story together at the table.
I'm considering doing a post about converting Pathfinder Modules into Factions and Fronts while keeping the spirit of the adventure alive (if not the strict plot). Let me know if this is something you'd like to see!