Daisuke Goura is a central character in the story, serving as the narrator and a key protagonist. He is a young man in his early twenties, notable for his tall stature and strong, athletic physique, which often leads others to describe him with words like heavy or solid. This physical presence, however, belies a gentle personality and a deep, genuine interest in books, even though he is incapable of reading them in the traditional sense.

The core of Daisuke's character is defined by a unique condition he developed in childhood. As a preschooler, he was an avid reader who loved books, but after secretly exploring his grandmother's library against her wishes, he was severely scolded and struck. This traumatic event left him with what he calls a constitution, a condition similar to a phobia of printed text, which causes symptoms like dizziness and nausea when he tries to concentrate on reading long passages. Despite this limitation, his admiration for books never faded, leaving him with a desire to be near them and learn about them through other means.

His motivation to become involved with the antiquarian book world is born from a combination of circumstance and personal history. After graduating from university, he finds himself unemployed when a job offer falls through. His grandmother has recently passed away, and his mother asks him to have a collection of her old books appraised, including a copy of Natsume Soseki's And Then that bears a mysterious signature. This errand leads him to the Biblia Antiquarian Bookshop, where he meets the shy but profoundly knowledgeable owner, Shioriko Shinokawa. She not only appraises the book but also unravels a secret from his grandmother's past that is directly connected to his own reading phobia. This revelation and her deductive skills draw him in, and he is subsequently hired as a part-time clerk.

In the story, Daisuke acts as the hands and feet of the bookshop's owner. Because Shioriko is introverted, reclusive, and physically unassuming, Daisuke takes on the role of her protector and agent in the field. His strong physique and his mastery of judo, which he practiced in university, make him capable of physically intervening in dangerous situations, gathering evidence, and confronting individuals involved in the various book-related mysteries. He is the grounded, practical force that complements Shioriko's brilliant theoretical deductions, often using his sharp intuition and common sense to piece together the human side of the puzzles she solves.

His key relationships are central to the narrative. His bond with Shioriko evolves from that of employer and employee to something much deeper. Initially, he is captivated by her beauty and her singular passion for books. As they work together, he grows to appreciate her inner strength and vulnerability, leading to a romantic relationship. His straightforward and honest personality often clashes with her stubborn and reserved nature, but this dynamic ultimately helps them both grow. Daisuke also has a close relationship with his mother, with whom he lives on the second floor of the family building after his grandmother's death.

Throughout the series, Daisuke undergoes significant personal development. While his reading condition does not fully disappear, he shows gradual improvement, with his mother noting he can read for longer periods than before. His emotional journey is marked by his growing confidence and his commitment to Shioriko. He overcomes professional doubts and personal conflicts, eventually confessing his love and, by the end of the story, proposing marriage, which she accepts. His most notable ability is his physical strength and judo prowess, which he uses for protection and investigation. However, his most important trait is perhaps his intuition, empathy, and unwavering loyalty, which allow him to understand and support those around him in ways that pure book knowledge cannot.