So the way the style works is onne person strictly plays an OC that they control, and if they have to, will also control some NPC's to move the post along, while the other person handles the role as "mod" and control the world itself. It's like saying the person playing the character is the "main character" in a video game, while the mod is the "GM" presenting the situation for the player to encounter, react to, and move on from.

Both roles are equally as important, and fun in my opinion, for various reasons. While the mod "controls" the world, the player gets to input their actions that determine how events will go, and maybe even create a new and unique situation the mod wasn't planning for, while the mod has to present situations to a character and based off their actions, move the plot and events into a certain directions.

1 person is the main character, the other person controls the world itself and how it reacts to the main character, and both roles build off what the other does. The world presents a situation, the player reacts in a certain way, based on their actions new events/paths become available while other options become closed.