This is an original story not from the book. The keyword in the story is "a meeting over time".

Always alone at school, Yamasato was able to live away from reality by writing his fantasy stories in his notebook. In the story, he is the center of the world, and the heroine, by default, is Ai (Hashimoto Ai), the popular girl at the school. But one day when he opened his notebook, he found the rest of the story he had never written...