Houzuki Ayano

A girl of mysterious circumstances who agrees to be adopted by Daichi. She seems to already know Kaede. When she is adopted, she becomes the eldest daughter of the Houzuki family and the others call her onee-sama or nee-san.

Her hair is a different length in the CGs than it is in sprites.

Spoiler

If she is chosen to inherit her step-father's estate, she runs away and becomes a prostitute. Unfortunately one of her clients recognizes her as a girl he once abused under orders from her father and reports her for money.