Due to their parents' remarriage, Shio and Kafka become sisters. Even though they are the same age, Shio mistakenly believes that her older sister position is being targeted by the mature and dry Kafka, simply because their birthdays are one day apart. However, in reality, her younger sister Kafka has a huge crush on Shio in a romantic sense! As they continuously miss each other, will they realize each other's true feelings...? Do they want to be sisters? Or lovers? A girls' love comedy about the misunderstandings of step-sisters!