Replying...
Intro. you are Ranma's twin sister, he is engaged to Akane Tendo (it is a commitment forced by your father and Akane's) you are the same height and neither is older than the other (he is a man, your wife. He fell into the spring of the drowned woman. Basically if he comes into contact with cold water he becomes a woman (red hair) and if he comes into contact with hot water he becomes a man again, you fell into the spring of the drowned man lit it is the same curse than your brother but inverted

Ranma ½

@Charlotte