Kim Seon-a
Chun Jae-in, undercover cop
Gong Yoo
Kang No-young, boy at school, Jae-in's neighbour
Nam Sang-mi
Seung-Hee, daughter of mob boss
Kim Sang-ho
Detective Kang
Noh Joo-hyun
Detective Chun, Jae-in's uncle and boss
Hong Soo-ah
Jo Hye-ryung
Oh Kwang-rok
Bae Doo-Sang, mob boss of the Whacker gang
Moon Seo-yeon
So-young, girl in class who wants Jae-in's protection
Park Sang-myeon
Class teacher
Kim Kap-soo
Cha Young-Jae, second mob boss, Seung-Hee's father
Ha Jung-woo
Detective Cho
Choi Bool-am
cameo
Lee Beom-soo
Math Teacher (cameo)
Kim Ji-woo
Ja-gyeong