Ippei Mihira is the grandfather of the series' protagonist, Sanpei Mihira, and serves as a foundational figure in the young boy's life and passion. Residing with Sanpei in the nature-rich, mountainous regions of Akita Prefecture, Ippei is well over sixty years old. He is a master craftsman of traditional Japanese fishing rods, a skill that has made him highly respected and well-known among anglers. His expertise, however, extends far beyond the physical craft of rod-making; he is also a master fisherman who acts as Sanpei's primary teacher and mentor. He is responsible for instructing his grandson not only in the external techniques and practical skills of fishing but also in its deeper, more spiritual aspects, often conveying these lessons through a combination of gentle guidance and rigorous challenges.

In terms of personality, Ippei embodies a simple and broad-hearted nature. His outward appearance is characteristically marked by wearing a chanchanko, a traditional Japanese sleeveless haori, over his other clothes. He lives a quiet life in the countryside, but his presence looms large in the story as Sanpei ventures out to various rivers, lakes, and oceans, demonstrating the techniques inherited from his grandfather. The central relationship in his life is undoubtedly with his grandson, Sanpei. Ippei’s role is that of the wise and patient elder who shapes Sanpei's destiny, encouraging the boy's natural talent for fishing and helping him to grow through numerous contests and encounters with rivals and companions.

Regarding his development, the most significant event attributed to Ippei Mihira occurs at the conclusion of the original manga narrative. In a moment of profound gravity, Sanpei returns home to find that his grandfather has passed away, discovered still holding a fishing rod in his hands. This event represents the end of an era for the character and a pivotal, sorrowful turning point in the story of his grandson. Prior to this, his notable abilities are clearly defined: he is a preeminent rod maker, a master of fishing techniques, and a wise spiritual guide, dedicating his later years to nurturing the prodigious talent of Sanpei.