This is an idea I've had for a while. I've always been a fan of CYOA (Choose Your Own Adventure) stories, where you read a sentence or paragraph, choose an option, and then follow on to read the consequences of your choice.
What this gig aims to do is to give you a spur of the moment interactive story, spurred by your personal preferences.
Together, we decide you would like a fantasy adventure story where the aim is to rescue the princess from the castle. (Or something to that effect.) We decide on the tools you will take, and the element of "risk" you want your choices to give you. Oh, and the genre/rating of the story. (Horror, 18+ or Young Adult, ASR rated, for example.)
Afterward, I will write the progression and choices on the go, and you will select whichever choice you desire each time. (I will also plan ahead in the times you are not there to continue it.)