The main heroine of the series, she is a quiet, fragile and reclusive girl, and fraternal twin sister to the main protagonist. Cursed with illness and frailty since birth, Sora was denied the sort of independent life that many take for granted. Yet beneath Sora's angelic doll-like appearance lies a troublesome personality that’s prone to withdrawn laziness and demonstrates a rather severe lack of social graces. In all honesty, Sora doesn't care for anyone else, and would much rather just surf the Internet and eat instant food, for as long as Haruka is always by her side.
Source from Wikipeida