Dr. Tofu Ono is the proprietor of a chiropractic and acupuncture clinic in the Furinkan neighborhood, serving as the go-to physician for the local community, including the Tendo family. He is a tall, handsome, and generally composed man who presents a professional and serious demeanor when tending to patients. However, this calm exterior masks two distinct and quirky traits. The first is his fondness for his full-size human skeleton model, which he has affectionately named Betty and often treats as a companion during consultations.

The second and most defining aspect of his personality is his complete and utter inability to function normally in the presence of Kasumi Tendo, the eldest daughter of the Tendo family. Dr. Tofu is deeply in love with Kasumi, but his feelings manifest as an extreme nervousness that causes his glasses to fog up and his rational mind to shut down. When Kasumi is near, he becomes a danger to himself and others, engaging in bizarre behavior such as dancing through town with Betty on his back, tearing up important medical books, or accidentally injuring his patients. The neighborhood residents have learned to avoid his clinic whenever Kasumi is known to be visiting, often remarking that he is usually such a good doctor. Kasumi herself seems completely oblivious to the effect she has on him, casually dismissing his odd actions as she does with most of the chaos around her. His infatuation with her has been present since Akane was a young girl, and in the anime, his mother reveals this tendency to lose control around a loved one is a family trait inherited from his father.

Academically, Dr. Tofu is exceptionally knowledgeable about human anatomy, rare acupuncture points, and traditional moxibustion techniques. His skills as a healer are profound enough to treat severe martial arts injuries, and he possesses a library of ancient texts on the human body. Beyond his medical practice, he demonstrates a deep, practical understanding of martial arts. Though he almost never engages in combat, he is able to use his knowledge of pressure points to paralyze opponents or to subtly influence people for their own good. On one occasion, he struck Ranma in such a precise manner that both of the young martial artist's legs gave out at an exact, predetermined time. Ranma himself acknowledges that Dr. Tofu is skilled enough to conceal his presence completely.

As a character, Dr. Tofu is most prominent in the early stages of the narrative. He serves as a trusted advisor and a catalyst, often gently pushing Ranma and Akane toward a better understanding of one another. He was also Akane's first love, a crush she held due to his kind and competent nature, a fact he remains unaware of. In a significant departure from the manga, Dr. Tofu’s role is somewhat expanded in the anime adaptation, where he participates in original storylines and even engages in a small battle against a hermit, using his pressure-point attacks to paralyze his foe. In the original manga, however, his presence diminishes considerably after the twelfth volume, and he largely disappears from the story without explanation. Despite his sporadic appearances, Dr. Tofu remains a well-regarded figure, remembered for his exceptional medical talents, his surprising martial arts prowess, and the comedic chaos that ensues whenever his love for Kasumi overcomes him. For a time, he employed a transformed Genma Saotome, trapped in his panda form, and the Chinese Amazon Shampoo as assistants in his clinic.