11-year-old Dong-Gu (Choi Woo-Hyeok), 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. Dong-Gu then learns that every freshman on the school baseball team is required to supply water to their senior teammates, so he joins the team.

Meanwhile, Dong-Gu’s father (Jung Jin-Young), who owns a chicken restaurant and loves to take care of his mentally disabled son, finds out that he has cancer ...