Jigoro Inokuma is the grandfather of the protagonist, Yawara Inokuma, and a central figure in her life. A living legend in the world of judo, he is a seventh-dan master who famously achieved five consecutive championships at the All-Japan Championships, a feat that solidified his status as a giant in the martial art. His name itself carries the weight of judo history, being derived from Jigoro Kano, the founder of modern judo, and Isao Inokuma, an Olympic gold medalist. He has also authored a book titled "Judo is not achieved overnight," which has garnered him followers and influence throughout the judo world both in Japan and internationally. Outside of his athletic pursuits, he runs a chiropractic clinic.

Jigoro's most defining characteristic is his all-consuming, and often domineering, passion for judo. From a very young age, he recognized a prodigious talent in his granddaughter Yawara and dedicated himself to honing her abilities through rigorous, daily training. His grand ambition is to see Yawara win a gold medal at the Barcelona Olympics and subsequently receive a national honor award. This goal has become an obsession, and he devotes nearly all his energy to its realization, often acting as the primary catalyst for the series' plot.

In his pursuit of this dream, Jigoro reveals a personality that is manipulative, scheming, and relentlessly stubborn. He is not above using any method, no matter how underhanded, to trick, coerce, or force Yawara into competitions she wishes to avoid. He has been known to hatch elaborate plots, give a sly V-sign when one succeeds, and interfere in Yawara's personal life, particularly when she grows close to a boy like the reporter Kosaku Matsuda. His traditionalist and old-fashioned nature is reflected in his speech, and he holds a clear disdain for modern, Westernized customs. He has a tendency to inflate his own judo rank and championship record, which changes every time he mentions it. Despite his gruff exterior, he has a comical side, often being seen with a snack while watching matches, a habit he shares with his son, Kojiro.

The relationship between Jigoro and Yawara is the emotional core of his character. While he clearly loves his granddaughter, his authoritarian methods create immense conflict between them. Yawara dreams of a normal life, away from the judo dojo, and her grandfather's pressure is the primary source of her frustration with the sport. Jigoro sees her talent as a gift to be used for athletic glory, while Yawara sees it as a burden that prevents her from being an ordinary girl. This dynamic creates a constant push-and-pull, with Jigoro acting as the primary antagonist to Yawara's plea for a normal life.

His role in the story is that of the mastermind and driving force. It is his decision to set up a rival for Yawara that introduces the wealthy athletic prodigy Sayaka Honami, sparking the main competitive rivalry of the series. He is the one who constantly pushes Yawara into the limelight and onto the national stage, ensuring that her path leads inexorably towards the Olympics. Without his relentless schemes and unwavering pressure, the events of the story would never unfold.

Despite his advanced age and small stature, Jigoro remains an incredibly formidable judoka. He maintains the ability to effortlessly throw active heavyweight judo players, demonstrating his superior technique is not a thing of the past. His personal judo philosophy is one of aggressive, overwhelming offense: he often states that a victory is not truly a victory unless it is won by an ippon, a perfect throw. He preaches the principle of "ju yoku go o seisu" or "softness controls hardness," but his own style is to dominate his opponent directly. He even demonstrates his skills in other areas, such as comically using a mix of judo and karate moves on a disco dance floor. He is a miniature, white-haired old man who embodies the spirit and physicality of a champion, making him a formidable and unforgettable presence in the world of Yawara!.