Doctor Ono Tofu is the local chiropractor in the Furinkan district, running a clinic known for acupuncture and moxibustion treatments. He is a tall, handsome young man, likely in his mid to late twenties, who has served as the trusted family doctor for the Tendo household for many years, having known Akane since she was a small child. As a physician, Doctor Tofu is highly knowledgeable, serious, and professional, demonstrating a deep understanding of human anatomy, pressure points, and esoteric martial arts techniques. He is respected by the community and is known for his exceptional skill in treating injuries, which are frequent among his acquaintances. Outside of his medical practice, he is easygoing and kindhearted, often displaying a playful side by giving his full-size skeleton model a name, Betty, and treating it as a companion.

Doctor Tofu’s most defining characteristic is the overwhelming and comical infatuation he has with Kasumi Tendo, the eldest Tendo daughter. Under normal circumstances, he is a pillar of competence, but the mere sight or mention of Kasumi causes a complete personality shift. His glasses fog over, he loses all sense of direction, becomes irrational, and performs bizarre and often dangerous actions, such as dancing through town with Betty on his back, twisting a patient’s spine in impossible ways, or destroying property. These antics are so well-known that local residents have learned to avoid his clinic whenever Kasumi is present. Ironically, Kasumi herself is completely oblivious to the effect she has on him, usually dismissing his strange behavior with her usual calm and casual demeanor. His mother, Kin Ono, appears in the anime and reveals that this tendency to lose control in front of one's beloved is a family trait inherited from his father.

In the early part of the story, Doctor Tofu plays a significant role as a mentor and ally to Ranma Saotome and Akane. He is one of the first people to recognize the potential in Ranma and Akane’s reluctant engagement and subtly uses his skills to nudge them closer together, such as once pressing a point on Ranma’s leg to make him collapse so Akane would have to carry him home. His expertise is invaluable when the group faces opponents who use advanced martial arts techniques. He is instrumental in helping Ranma find cures for powerful attacks like Happosai’s Moxibustion and Cologne’s Full-Body Cat Tongue technique, using his knowledge of acupuncture and rare medical lore to identify weaknesses and direct Ranma toward solutions. For a time, he also employs Genma Saotome, who works off his debts as an assistant in panda form, and later employs Shampoo as a nurse before she leaves to work at the Cat Cafe.

Regarding his martial abilities, while Doctor Tofu is never seen engaging in a full-fledged fight in the manga, he is implied to be a highly skilled martial artist. Akane has stated he is a good fighter, and Ranma himself admits that Tofu is skilled enough to sneak up on him, a feat very few can accomplish. In the anime, he briefly demonstrates his combat prowess by using his precise knowledge of pressure points to completely paralyze an opponent and his group of trained frogs. This has led many to believe he would be a formidable fighter if he ever chose to be.

Doctor Tofu’s presence in the narrative diminishes significantly as the series progresses. He disappears entirely from the manga after the twelfth volume with no explanation, though he makes a cameo appearance in the final volume’s group illustration, sitting on a picnic with Kasumi. The anime expands his role slightly, giving him a few more comedic episodes focused on his relationship with Kasumi and his matchmaking mother. Despite his eventual departure from the main story, Doctor Tofu remains a memorable character, notable for his sharp contrast between being a brilliant and reliable physician and a love-struck fool, as well as for being an early and crucial source of support for Ranma and Akane.