It is known that Dr. Tofu Ono loves Kasumi Tendo, the eldest of the Tendo family's daughters. Whenever Kasumi is not around, Ono is just himself, happy and calm. But, whenever Kasumi comes in his office for some reason she insists, Tofu becomes insane. In episode six, Ranma gets struck in the face by Akane Tendo, Kasumi's sister. As Tofu is helping straightening Ranma's nerves, Kasumi comes in to return a book to Tofu. Tofu's glasses start to shine, then he starts to get crazy. Tofu randomly starts stretching Ranma in uncomfortable ways, making Ranma scream in pain.
Another example, is in the episode when Tofu's mom comes to his office and stays for a while. While Mrs.Ono is there, she tells Tofu it was time to get married. Tofu agrees, but his mom gives him choices. Akane feels sorry for Tofu, so she offers to be his bride. Mrs.Ono accepts. Meanwhile, Ryoga Hibiki sees the whole thing. So, he goes to Ranma, and explains what he saw. Ranma turned into a girl, and also offered to be Tofu's wife. Then, Nabiki comes in, and offers as well (of course, for Tofu's money). When Mrs.Ono, comes in, Tofu smiles, and rushes to her. But, he bumps into the door beside Kasumi. Then, Tofu, says he will chose his bride. He is about to say Kasumi, but says Betty instead (another one of his ways of being crazy). Mrs.Ono remembers her husband, looking like Tofu. Mr.Ono was exactly like Tofu. So, Mrs.Ono leaves, and trusts Tofu to make the right choices for his bride.
Tofu's crazy ways when Kasumi's around includes:
-Losing sense of direction.
-Bumping into stuff.
-Dancing with his skeleton, Betty.
-Spilling stuff he is holding.
-And, usually, making things worse for Ranma if he really needs Tofu.
Kasumi has some hints that she loves Tofu. In the end credits called Red Shoe Sunday, Kasumi sang about loving Tofu. Another hint is that she loves the weird-type guys. However, the lyrics to Red Shoe Sunday are not confirmed to be canon, and are left as speculations.
Unfortunately, Dr. Tofu was abandoned as a character after the first third of the manga series and their relationship was never officially elaborated further. Though Tofu cameos on the final spread for the final volume, on a picnic with Kasumi.
Tofu continued to appear in the anime where his relationship with Kasumi received some focus.