The three-dimensional world referred to the real world, which was the virtual world created by the author, such as novels, animations, games, and so on. The three-dimensional concept that the girls used to refer to usually meant that the world we live in in the real world is different from the virtual world in the novel, so we may feel different emotions and experiences. In the eyes of the original girls, the 3D world was real. They could really feel the plot and characters in the novel and interact with the author.