As a functional process, I’ve done the following when dealing with the RS.
What direction(s) does the *RS(s) move in my story?
- together (boy gets girl)
- apart (boy loses girl)
- together-apart-together (boy gets girl; boy loses girl; boy gets girl) (boy gets wrong girl; boy loses wrong girl; boy gets right girl) (boy gets right girl; boy loses right girl; boy gets wrong girl)
- apart-together-apart (boy is alone; boy gets girl; boy loses girl)
- together-together-together (us vs. the world)
- apart-apart-apart (not in a million years)
*more than one relationship could be part of the RST
What adjective or phrase best describes the RS status?
- hanging on by a thread
- bliss
- settling for less
- et cetera
What’s the nature of the relationship?
- familial
- love
- teacher/student
- et cetera
What’s the intensity of the relationship?
- slow and steady
- roller coaster ride
- low heat
- et cetera
A change in the status, nature, direction or intensity of the RS can be accomplished by a believable beat. When reasonable, a double duty beat can push the MC (OS, IC) in the direction that I want, and – for example – a consequence of the MC (OS, IC) beat could push the RS in the direction along its path.
It is useful to create a snapshot of my RS at various points in the story (keyframing as Jim says) then try to believably manipulate these categories into that direction. This can be accomplished through a gradual shift during a long sequence or a hard beat that happens within a scene.
For me, calling the RS a character is useful only because it forces me to remember that the relationship should have characteristics that are definable, measurable, alterable, and so on.
I have no doubt that my terminology will evolve and this process might become more automatic, but this is what I currently use.