Twin sisters, Arisa and Tsubasa, are separated by their parent's divorce. The twins secretly exchange letters with each other during their separation. They are finally united after three years and Arisa asks Tsubasa to pretend to be her and spend a day in her school just for fun. At school everyone seems very nice to Tsubasa (who is pretending to be Arisa) and everything seemed normal... until she finds a strange note in her sister's shoe locker. When Tsubasa hands over the letter to Arisa, Arisa tries to kill herself by jumping out of a window. Arisa survives but remains in a coma. The letter read, Arisa is a traitor. After her sister's suicide attempt, Tsubasa is determined to unravel the mystery behind the letter and her sister's suicide attempt so Tsubasa continues to go to school as Arisa... will she find out who sent the note and why it had such an effect on Arisa?