Hazuki Shinonome

She is a teacher and a club adviser of the Food Research Club, she is such a drunkard that she keeps her own beer keg in the club and would often drop by to have a mug or two. Though she is Satsuki's elder sister, she never gets any respect from her. It is later reveled that she and Satsuki are actually half-sisters. *She initially believed she was the daughter of her father's first wife, but she later discovers that she is in fact the illegitimate daughter of her father's then-mistress. Her father's first wife later dies and he marries his mistress, who later gives birth to Satsuki. Upon realizing this, Hazuki became depressed and left the family.

It is also revealed that Yuki would sometimes drop by to cook and have meal with her, because she is quite a bad cook. It is also suggested that she has feelings for Yuki, but it is not known as to how deep her feelings are for him. (Source: Wikipedia)