http://www.furinkan.com/takahashi/takahashi2.html
Takahashi:[...]There are three essential elements to the series: Ranma, fighting, and romance. Which story was fun to draw? I like them all. I want to draw a manga you can laugh at and enjoy reading, so I tried to include a lot of gags in every episode. I really enjoy drawing something like a "promise" gag, where a character grows tired and just goes flying off. Since the serialization was long, it could have grown tiresome if it were just "fighting, fighting" or "romance, romance" so after a fighting sequence I might draw a brieft gag episode, followed by a romantic story... in order to create the freshest Ranma, I did some rotation [of the stories].
http://www.furinkan.com/takahashi/takahashi10.html
Question: So when it comes to writing your stories, be it Inuyasha or Ranma, the ending are not set beforehand, are they?
Takahashi: No, they are not. It's better if I think about it on the spot. To force your characters to go in a direction that you have preconceived- that manga will most certainly not be fery interesting. What you think is best on the spot, right before you take a step and go forward and make the path- I think that is what creating manga is all about. That's the best way for me to create manga.