11-year-old Dong-ku, who is mentally-challenged, is the school's water boy until the school installs a water purifier system. Disappointed, Dong-ku soon learns that the school's baseball team needs a water boy, so he decides to join the team.

Filling classmates' cups with a kettle is the only work 11-year-old Dong-ku, who is mentally challenged, can do in his school life. However, even this small connection with the outside world breaks as one day a new water purifier replaces the kettle in his classroom. Disappointed badly by losing his only hope to survive in a regular school, he finds that every freshman in the junior baseball team is required to supply drinking water to other members with a kettle. Though he knows nothing about baseball, Dong-ku decides to join the team while his father, Jin-kyu, struggles to save his kids-only shelter, their chicken bar.