Yeo Jin Goo as Jung Jae Min
– Song Eui Joon as Jae Min (young)
Seol Hyun as Baek Ma Ri
– Han Seo Jin as Ma Ri (child)
Lee Jong Hyun as Han Shi Hoo
– Kang Han Byul as Han Shi Hoo (young)
– Song Joon Hee as Han Sho Hoo (Child)
Gil Eun Hye as Jo Ah Ra

Family

Yoon Ye Hee as Song Sun Hwa (Ma Ri’s mother)
Ahn Kil Kang as Baek Seung Hoon (Ma Ri’s father)
Jo Yi Hyun as Baek Joseph (Ma Ri’s younger brother)
Lee II Hwa as Kang Min Ha (Jae Min’s mother)
Jo Min Ki as Jae Min’s father
Song Jong Ho as Han Yoon Jae (Shi Hoo’s uncle)

Classmates

Oh Kyung Min as Choi Soo Ri
Park Gun Tae as Hwang Bum Sung
Lee Da Heen as Ae Kyung
Kim Ji Ah as Yoon Min Sun
Lee Yoo as Ah Ra and Ae Kyung’s friend

Others

Joo Ho as biology teacher
Kim Sun Kyung as Won Sang Goo
Byun Gun Woo
Park Sun Woo
Im Sung Uhn as homeroom teacher