Although the word derivative commonly implies imitation, that is not exactly the meaning here. Derivative fundamentally means "comes from another thing". In this case, the "thing" it is coming from is the narrator.
It means that narrative comes from the perspective of the storyteller in order to develop the relationship with the audience.
In my opinion, the word "derivative" was a poor choice in writing. It technically has the right meaning, but is very confusing even for native speakers.