Dr. Tofu Ono is the young, kind-hearted chiropractor who runs a clinic in the Furinkan neighborhood, located conveniently close to the Tendo Dojo. He serves as the family doctor for the Tendo household and has known them for a very long time, watching the Tendo sisters grow up from a young age. Dr. Tofu is a tall, handsome young man who presents a professional and reliable exterior, being very knowledgeable and serious when it comes to medical matters. However, this composed demeanor is dramatically and humorously counterbalanced by his intense infatuation with Kasumi Tendo, the eldest Tendo daughter. Whenever Kasumi is near, or even just mentioned, his glasses fog over and he becomes a bumbling, irrational mess, completely losing focus on his surroundings. This can make him a danger to himself and his patients, leading to incidents where he might twist a patient's neck incorrectly or even dance through town with his skeleton model on his back after a phone call with her. This nervous trait is, according to his mother Kin in the anime, a family characteristic shared by his father. Despite this odd behavior, Kasumi remains mostly oblivious to the effect she has on him, and for a time, Akane Tendo harbored a childhood crush on him, which he was also unaware of.

Away from the chaos of his love life, Dr. Tofu is a calm and friendly individual who is well-liked by the community, particularly his older patients. He often punctuates his professional talks by playfully interacting with a full-size skeleton model he calls Betty. His primary motivation stems from his medical practice and a genuine desire to help others. He acts as a key supporter and advisor, especially in the early parts of the story, possessing an extensive and esoteric knowledge of martial arts techniques, pressure points, moxibustion, and acupuncture. He is one of the first characters to recognize the potential in Ranma and Akane's relationship and skillfully nudges them together, demonstrating a thoughtful, behind-the-scenes role. Beyond relationship advice, he provides crucial medical and technical aid to the main characters. For instance, he heals their injuries, helps Ranma find cures for techniques like the Full-Body Cat's Tongue and the Ultimate Weakness Moxibustion, and even secretly strikes a pressure point on Ranma to temporarily paralyze his legs, forcing a more friendly interaction with Akane.

While generally a pacifist who relies on his medical knowledge, Dr. Tofu is also a remarkably skilled martial artist, though he is never seen practicing. Both Akane and Ranma acknowledge his ability, with Ranma admitting that Tofu is skilled enough to sneak up on him and hide his presence completely. His combat style, when he chooses to employ it, relies on his profound understanding of the human body, using precise pressure-point attacks to paralyze opponents or cause delayed effects with pinpoint accuracy. In the anime, he demonstrates this in a brief battle against a frog hermit, using his knowledge to paralyze his foe completely. Because of this, he is considered by fans to be one of the most potentially formidable martial artists in the series.

Dr. Tofu's role in the story is most prominent in the early volumes, where he acts as a mentor figure and a source of wisdom. As the series progresses, his appearances become less frequent, and he eventually disappears from the manga after volume 12. The anime adaptation expands his role slightly, giving him more screen time in original stories, such as an episode where his mother tries to find him a bride and another where he attempts to take Kasumi on a date to an amusement park. Despite his reduced presence in later material, he remains a beloved and iconic character from the series' early days.