A veteran detective of the National Police Agency for 7 years and the partner of Park Sun-ho. He "resets" his life by one year after his partner was killed by a criminal.
A webtoon artist of the webcomic series "Hidden Killer" for the past 3 years. She "resets" her life by one year after she suffered from an accident that left her in a wheelchair.
One of the ten people who "reset" their life. She "resets" her life after feeling guilt for causing Shin Ga-hyun's accident that left her in a wheelchair. She is later killed by Park Sun-ho which was disguised as an accidental death on the stairs.
A cafe owner who is later revealed to be a professor in a hospital and the mastermind behind the "reset" project. He "resets" his life to experiment with the other nine candidates to see who survives. He is later arrested by Ji Hyung-joo in the next "reset".
A security guard. He "resets" his life to earn money from lottery wins for his wife. He is later killed by Park Sun-ho which was disguised as a heart attack.
Jung Min-sung as Cha Jeung-seok
A stockbroker. He "resets" his life to fix his mistakes on stock exchanges. He is later killed by Park Sun-ho which was disguised as a suicide.
A pro-gamer and the son of the nominee for the Minister of Education. He "resets" his life to prevent his past from ruining his father's career. He is later killed by Park Sun-ho to frame his partner Ji Hyung-joo for murder.
A university student who suffers from Munchausen syndrome. She "resets" her life to make up with her boyfriend. She is later killed by Park Sun-ho and her body was abandoned in a manhole.
A Police Lieutenant of the National Police Agency and Ji Hyung-joo's partner. He is revealed to be the serial killer detective and started killing after being promoted to Lieutenant during his 12-year service. He is later arrested by Ji Hyung-joo in the next "reset".
Shin Ga-hyun's best friend who cheated with Ga-hyun's boyfriend. She is later killed in a hit-and-run incident caused by Seo Yeon-soo's husband.
Im Hyun-soo as Han Woo-jin
Shin Ga-hyun's boyfriend who cheated on her with Min Joo-young.
Others
Kim Ha-kyung as So Hye-in
A florist and flower shop owner. She was a candidate for the "reset" but refused to participate after finding out she would not be pregnant at the time. She is later killed by Park Sun-Ho which was disguised as an arson case.
^ abIn order to circumvent Korean laws that prevent commercial breaks in the middle of an episode, what would previously have been aired as single 70 minute episodes are now being repackaged as two 35 minute episodes, with two episodes being shown each night with a commercial break between the two.[1]
^Due to some ratings not recorded, the exact average rating is unknown.