Sinner's Blood (Fixing later, Need to change the plots)

Hikari Chiyo, The patient with strange blood disease but without any sign of illnesses, Have been discharged from hospital. Hoping to find joy she have been longed for, along with her best friend, Ryouhei. However on that day, the unknown virus spread all over the whole city and exterminate everything. Her beautiful day suddenly changed forever... Is this a curse? Or the beginning of the Unfortunate road? Which fate lie ahead? *Note* This novel might looks related to Guilty Crown(Visual Novel). But it's not actually second season or something! Do not be confused!