Nanai, also known as Asahiko Kakei, is a supporting character in the anime A Good Librarian Like a Good Shepherd. He is a third-year student at Shiomi Academy, where the story takes place, and is a member of the school's Library Club. He is easily recognized by his grey hair and grey eyes. Nanai is known for his serious and stoic demeanor, which has earned him the nickname iron wall from his friends. Despite this reserved exterior, he possesses a kind heart and cares deeply for those around him. He is highly independent and self-sufficient, often preferring to work alone rather than rely on others. He has a strong passion for research and intellectual pursuits, frequently spending long hours in the library reading and studying. He values order and structure, approaching his tasks with practicality and attention to detail.

Nanai is motivated by a genuine dedication to his responsibilities as a library club member and a desire to obtain knowledge. In the story, he plays a supporting role, helping the protagonist Kyoutarou Kakei understand the workings of the Library Club and uncover the hidden secrets of the academy. His expertise in library science, including cataloging and archiving, proves valuable to the group's efforts. He often serves as a source of guidance and stability for his peers, who respect his knowledge and reliability.

A key relationship in Nanai's life is his bond with Kana Suzuki, another member of the Library Club who has been his friend since childhood. He is protective of her and consistently looks after her well-being. While he is not the most emotionally expressive person, his actions show his loyalty and care. Over the course of the series, he remains a steady and trustworthy figure, offering knowledge and support to the other characters without seeking recognition for himself.