The first "the" signifies a general statement about the class of things called "ballads". Cf.
1. The cat is a furry quadruped with some very strange habits.
— i.e. cats in general are furry quadrupeds, etc.
The second "the" signifies "something that may easily be inferred from the context": "story" is already implied in "narrative".
(That said, the indefinite article would have sounded ok in both positions.)