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

Cha Ah-reum