Two elementary boys, who are best friends and baseball fanatics, had to be separated as one left Korea to pursue education abroad. Many years later after returning to Korea for high school, the boy had found his best friend to have only turned into a girl instead.

알 수 없는 이유로 성별이 변한 고등학생 '신해윤'이 소꿉친구 '강태주'와 재회하며 시작되는 두근두근 하이틴 판타지 로맨스