I was reading some interviews with Rumiko Takahashi featured in some recent Ranma 1/2 reprints.
Translated here:
https://kanabits.wordpress.com/2018/02/22/the-making-of-ranma-interview-archive/
Interesting stuff:
The Making of Ranma, Part 1: Ranma Saotome
— So the basic idea is water turns Ranma into a woman, and hot water turns him back into a man. Where did this come from?
Takahashi: I was looking for a way to make it possible for him to be able to go back and forth between genders. I came up with a number of ideas along the way, but in the end, nothing was very entertaining.
— Was the idea of Ranma's gender-bending there from the beginning?
Takahashi: It was, but I just couldn't figure out how he would do so. But then I had a kind of vision of a bath-house's cloth entrance sign.
— You didn't actually see the sign with your own eyes.
Takahashi: No, I didn't. It just kind of popped into my head.
— And why did you decide to make it a martial arts story?
Takahashi: Gender-bending was the starting point. Then, the idea of water turning Ranma into a woman and hot water turning him back into a man. Next, I had to decide where this gender-bending ability would come from. This led to the idea of a cursed spring, and when I thought where you might find one, I thought of China. And when I thought of China, I thought of martial arts. It all kind of came to gather in that order.
— So the gender-bending was the basis, and the martial arts was added later.
Takahashi: That's right. Once the water and hot water thing was decided, everything else became a lot easier. Also with the idea that if you almost drown yourself in Jusenkyo, you could become just about anything.
— How did you come up with Ranma's character design?
Takahashi: This also got a lot easier after I decided on the gender-bending and Jusenkyo being in China. The traditional Chinese clothes I chose are surprisingly unisex. And China also made me think of ponytails, which again work with both genders.
— Ranma's ponytail is pretty iconic.
Takahashi: Exactly. I knew I wanted him to have one. Or perhaps it was more that I wanted readers to see that ponytail and, whether the ponytail was attached to a boy or a girl, immediately know they were looking at Ranma. Picking China as an influence was a great choice.
Part 2: Ryoga Hibiki
His terrible sense of direction is what made him so strong?!
— Ryoga is self-taught, but he's pretty strong.
Takahashi: In the world of Ranma 1/2, all characters are gifted martial artists.
— He also has a terrible sense of direction.
Takahashi: In the beginning I brainstormed a number of defining characteristics for him—for example, him being awkward around women—but nothing really made for a good character. But one day I was thinking how wonderful people are who, regardless of their mistakes, can keep moving forward in life, and from that, I decided to give him a terrible sense of direction. Along with that, I could do gags with souvenirs of his travels and other stuff and I think it worked out really well. Oh and, going back to what you said about Ryoga being so strong despite being self taught…don't you think he got that way because his experiences getting lost, wandering and camping out in the wilderness are what toughened him up? I mean, he wouldn't be able to find his way home even if he wanted to!
— Speaking of which, Ryoga's home is surprisingly normal.
Takahashi: I dunno, it just felt like that's how it should be.
— And his dog's design is quite something.
Takahashi: Yeah, I love that design.There's no way a dog like that could exist, which is why I thought it was such a perfect choice.
— Did you create Ryoga with the purpose of him being a rival to Ranma?
Takahashi: Well, at the time I thought it would be nice if it worked out that way. I had a number of Kuno-like characters there from the beginning, but Ryoga was the best choice for a rival, as he seemed to me the most likely to be able to remain one until the end. At the very least, I wanted him to be more than just a minor character who made guest appearances here and there.
— Because he's such a good character.
Takahashi: I worked hard to make him so.
— All the good characters end up falling in cursed springs, don't they?
Takahashi: I made sure in the beginning, especially, that the cursed springs would stay a part of the story and continue influencing its direction. The springs are really what Ranma 1/2 is all about.
— Why did you choose to make Ryoga a black pig?
Takahashi: I had already decided on making him a pig. Because when you think of Chinese food, you think of pork. But, no matter what, I wanted the design to be cute, and Meishan pigs (the breed used for China's highest quality pork) are definitely not. So I made him a black pig instead.