A boy falls to his death at school, but Ok Chan-mi does not believe that her twin brother, Park Won-seok, committed suicide. Chan-mi transfers to her brother's school, Yongtan High, and meets Ji Soo-heon, who witnessed her brother's death. A "hero," who avenges bullied students, appears at Yongtan High. Chan-mi speculates that it may be connected to her brother and starts looking for this hero.

• Shin Ye-eun
• Lomon
• Seo Ji-hoon
• Chae Sang-woo
• Lee Soo-min
• Chung Su-bin
• Kim Joo-ryoung
• Wooyeon