11-year-old Dong Ku, who is mentally challenged, loves going to school to provide water to his friends. However, he gets disappointed when the school decides to install a water purifier in every classroom. He finds that every freshman in the school baseball team is required to supply water to other members so he joins the team. Meanwhile, Dong Ku's father, who owns a chicken restaurant and loves to take care of his mentally disabled son, finds out that he has cancer and becomes hopeless.