Question

Characters advance the plot of a story through "blank" relationships, where their actions lead to results that move the plot along.
Fill in the blank

Answer 1

The question is asking to fill in the blank or supply the necessary word that could complete the said question, base on my research and further investigation, I Would say that the answer would be Individual Relationship.  I hope you are satisfied with my answer and feel free to ask for more 

Answer 2

The correct answer is cause-and-effect.

As the name itself says, cause and effect relationships have to contain a cause and an effect. A cause for an action is what motivates a character to do a particular thing, and the effect is the result of such actions. Obviously, these kinds of relationships could move the plot forward and give rise to new relationships and events within a story.