小日向 すもも

Sumomo is Yuuma's younger sister who seems to have an energetic personality. She has amazing cooking skills. She has known Haruhi since childhood and they used to play together. Due to family circumstances, Sumomo didn't become Yuuma's sister until after she had entered elementary school. She is not a blood-related sister for Yuuma. 

Taken from url=http://en.wikipedia.org/wiki/Happiness!#Characters