From Wikipedia:

Attacker You! is the story of ambitious and energetic thirteen year-old junior high schoolgirl You (pronounced Yoh) Hazuki, who moves to Tokyo from the Japanese countryside to live with her father Toshihiko, a cameraman recently returned from Peru, and attend school. You's mother is not in the picture, having left when You was very young. Also living with You and her father is her younger brother Sunny, who is very attached to his older sister and tends to follow her everywhere she goes, including to school and to her volleyball matches. However, You's father is not supportive of her volleyball playing, and You is puzzled as to why he gets so angry about it.