Twin sisters, Arisa and Tsubasa, are separated by their parents' divorce. The twins secretly exchange letters with one another 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 nice to Tsubasa (who is pretending to be Arisa) and everything seems normal - until she finds a strange note in her sister's locker!
