A popcorn novel is usually a light, easy-to-read, and often highly entertaining book that doesn't require a lot of deep thinking. It's like the literary equivalent of snacking on popcorn - enjoyable but not too heavy.
Most likely, the 'Popcorn Dancers' is fiction. Usually, when there's a title like this, it implies a made-up story or performance rather than being based on real events or people.
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.
When writing about the smell of popcorn in a story, think about using vivid words like 'fragrant', 'enticing', or 'intoxicating'. Describe how the smell lingers and spreads, creating a certain atmosphere.