I'm not very familiar with this specific 'cancion de pulp fiction'. But if it's related to 'Pulp Fiction', it might have a sense of coolness and edginess, similar to the movie's style.
I'm not entirely sure about the specific origin of 'cancion de pulp fiction'. It could be a song inspired by the movie 'Pulp Fiction'. Maybe it was created by a fan or an artist who was really into the movie's unique style and story. There could be a whole backstory to it that involves the cultural impact of the movie on the music scene.
Since we don't have much information about this 'cancion pulp fiction', it's difficult to determine the composer. It could be a local artist who created it for a specific event or a niche audience. Maybe it was made by a student of music as an experiment inspired by the 'Pulp Fiction' movie. There are so many possibilities.
Nezuko is initially 12 years old in the manga. As the story unfolds, her age doesn't change significantly in a traditional sense, but her character development is quite remarkable.