Legally, Dad is a 2020 Korean web drama about an orphan girl who is offered to be adopted by a stranger. Legal, Dad also known as Step Dad On Paper Original title 서류상 아빠 (Seoryusang Appa) Genre Romance Original release August 27, 2020 – October 1, 2020 Starring Choi Kyung Hoon as Sul Yoo SangLee Hyun Joo as Kim Ah YoungMin Se Woong as Yoon Joo HoLee A Ra as Kim Dan Bi Country of origin South Korea Original language Korean Number of episodes 6 Time slots Thursday KST Episode length 12 minutes Network Studio DIA Series Guide Previous Next N/A N/A Streaming Sites Studio DIA Orphan Ah Young is a financially struggling 23-year-old woman who cares for her 8-year-old sister Dan Bi while juggling part-time jobs. One day, a 28-year-old man, Yoo Sang, appears in front of Ah Young and offers to be his father through a signed agreement.