Actor: Han Sung-min Woo-seok Kim Won-bin Chae Yu-chan Kang
Everyone has an invisible boundary, which will change with their surrounding people and matters. Their boundaries limit to schools, tutoring classes and their parents. However, as they stepping into their 20s, new boundary will appear.
It is thought that once we are at our 20s, everything will be sound, but actually it is not.
At the age of 20, we are about to cross our boundary.