Kono Kanojo wa Fiction desu.  

This Girlfriend is a Fiction, この彼女はフィクションです。

The main character is a young man who has fallen deeply in love with an older woman who is widely regarded as a talented writer. So enamored is he that he has neglected his own secret passion, which involves writing detailed profiles of single women over the course of ten years. These profiles include information such as birth dates, personalities, hobbies, and conversations, all meticulously recorded in numerous notebooks. Despite the fact that this fictional character has served as both a friend and lover to him for this entire time, he has decided to discard her in order to "purify" his notebooks. To do so, he burned them at a nearby shrine. As fate would have it, the woman he is now deeply in love with also happened to be present at the shrine during the rainstorm. As they spoke, she confessed that she was struggling to write her novel due to inexperience. Emboldened by this revelation, the young man felt compelled to share his own secret with her. With courage, he reached into a bag and retrieved not only his notebooks but also the woman whom he had created over the past decade. Of course, she was completely naked.