Sora no Mannaka(2004)

Sora no Mannaka

Amasawa Miyako, the middle child of 5 siblings, is the only 'normal' one, the others all being very good-looking and very talented at something. She takes care of them at home with cooking, cleaning, etc. because their parents are very busy at work, but she has to deal with both her own insecurities and people's opinions on how she's not like her brothers and sisters. It also doesn't help that she likes her best friend who's in love with her older sister.