Cast

Main characters

• Kang Sora as Shin Hae-sung
• JB as Jang Woo-jae (I:dn Member)
• Jinwoon as Jin Yoo-jin
• Jiyeon as Rian/Lee Ji-kyung (HershE Member)
• Hyorin as Nana/Kim Jae-hee (HershE Member)
• Park Seo-joon as Siwoo (I:dn Member)
• Ailee as Ailee (HershE Member)

Kirin students

• Jr. as Jung Ui-bong(Ailee's boyfriend)
• Yoo So-young as Park Soon-dong
• Kim Jisoo as Park Hong-joo

Kirin teachers

• Park Jin-young as Yang Jin-man (English Teacher)
• Kwon Hae-hyo as Joo Jung-wan (Principal)
• Kim Jung-tae as Lee Kang-chul (President)
• Choi Yeo-jin as Ahn Tae-yeon (Vocal Teacher)
• Park Kahi as Hyun Ji-soo (Dance Teacher)

Extended cast

• Jung Yeon-joo as Lee Seul
• Yoon Hee-suk as Shin Jae-in
• Hwang Mi-sun as Rian's mother
• Jung Kyu-soo as Hae-sung's father
• No Jung-ui as Shin Hee-bong (Hae-sung's sister)

Cameos

• Kim Soo-hyun as Song Sam-dong (ep 1)
• IU as Kim Pil-sook (ep 1)
• Toxic as band performing with Yoo-jin in Hongdae (ep 1)
• MYNAME as OZ Entertainment idol group (ep 2)
• Boyfriend as themselves (ep 2)
• Psy as trainer coach (ep 5)
• Yeeun as herself (ep 9)
• miss A as themselves (ep 15)
• Park Jin-young as himself (ep 16)