At Deoksan elementary school under Woelaksan (Mt.), there are 15 children who have been in the same class for 6 years. They don't sit quietly in class like other school kids. After school, they gather at a hidden secret spot by the river, and they whisper, saying that the homeroom teacher is an adult who can't even control his emotions. Yoonjae, a new teacher who imagined that children would sit quietly in the classroom, is bewildered when he sees the children different from what he expected. The changing seasons with the children, and what will their sky be filled with?