"Diary of Our Days at the Breakwater" centers on Hina Tsurugi, a high school girl who moves to a small coastal town and joins her school’s Breakwater Club, a group dedicated to fishing. Initially unfamiliar with the hobby, Hina is introduced to the world of fishing by the club’s members, who each bring their unique personalities and expertise to the activity. The series explores the club’s daily adventures as they learn about different fishing techniques, tackle various challenges, and bond over their shared experiences.

The main characters include Hina, who starts as a novice but gradually develops a passion for fishing; Yuuki Kuroiwa, the club president and an experienced angler with a calm demeanor; Natsumi Hodaka, a cheerful and energetic member who often provides comic relief; and Makoto Oono, a quiet and knowledgeable member with a deep understanding of marine life. Together, they navigate the intricacies of fishing, from selecting the right equipment to understanding the behavior of different fish species.

The narrative is episodic, with each episode focusing on a specific fishing outing or challenge. The series emphasizes the educational aspect of fishing, often providing detailed explanations of techniques, equipment, and the ecological aspects of marine life. Through these outings, the characters grow not only in their fishing skills but also in their friendships, as they support each other through successes and failures. The coastal setting plays a significant role, with the serene and picturesque environment adding to the overall atmosphere of the series. The blend of lighthearted moments, character development, and informative content creates a balanced and engaging viewing experience.