Kayo Horikoshi

Jiro's younger sister. She's always admired her older brother. She wishes to move to Tokyo to study medicine, but her father refused. She soon became friends with Naoko and showed compassion towards her, blaming Jiro for her medical condition her lonely life. When she visited the Sanatorium as a nurse, she witnessed Naoko in an accident. When she finds the letter meant for Jiro from Naoko, she realized its true intentions and bent down weeping.