Ji Sung as Cha Do Hyun / Shin Se Gi / Perry Park / Ahn Yo Sub / Ahn Yo Na / Nana / Mysterious X
– Lee Do Hyun as Do Hyun (Child)
Hwang Jung Eum as Oh Ri Jin
– Kim Amy as Ri Jin (Child)
Park Seo Joon as Oh Ri Ohn
– Kim Ye Joon as Ri Ohn (Child)
Oh Min Suk as Cha Ki Joon
Kim Yoo Ri as Han Chae Yun

Do Hyun’s family

Kim Young Ae as Seo Tae Im (Do Hyun’s grandmother)
Shim Hye Jin as Shin Hwa Ran (Do Hyun’s mother)
Ahn Nae Sang as Cha Joon Pyo
Kim Yong Gun as Cha Gun Ho
Myung Se Bin as Min Seo Yun

Do Hyun’s helpers

Go Chang Suk as Suk Ho Pil (Psychiatrist)
Choi Won Young as Ahn Gook (Do Hyun’s secretary)

Ri Jin’s family

Kim Hee Jung as Ji Soon Young (Ri Jin’s mother)
Park Jun Gyu as Oh Dae Oh (Ri Jin’s father)

Ri Jin’s colleagues

Lee Shi Un as dr. Park
Jo Chang Geun as Dr. Kang In Kyu

Ki Joon’s family

Kim Na Woon as Yoon Ja Kyoung (Ki Joon’s mother)
Kim Il Woo as Cha Young Pyo (Ki Joon’s father)
Kim Hyun Joo as Baek Jin Sook (Chae Yun’s mother)