Neptune is a big blue planet that we know and study in real life, but sometimes people use it as a character in stories and movies. Think of it like a pretend friend; even though we know it's not real, we can still imagine it doing things and having a personality.
In some stories, Neptune might be the home of aliens or other creatures that we don't know about yet. These stories might show Neptune as a mysterious and magical place.
In other stories, Neptune might be a symbol for something else. Because Neptune is the planet associated with water, it might be used to represent the emotion of sadness or the power of the ocean.
Whatever the story, Neptune is a fun way to think about space and explore our imaginations.