One day, he meets a girl who came from the future named Kang Seo-hae, starred by Park Shin Hye. She is an elite warrior who has survival skills that she's learned from living amongst gangsters and warlords. She is able to fight men twice her size with her bare hands. She even knows how to make bombs and is good with guns. Her mission is to travel back in time and save Han Tae Sul and help him save humanity.
"Sisyphus: The Myth" Episode 7
The previous episode of the drama (Episode 7) started with Kang Seo Hae waking up and discovering she's wearing a different dress. She immediately noticed that her wound is healed and that she's at Choi Jae Sun's (Chae Jong Hyup) house. She recalled what happened the night before and how she ended up there. When she mentioned Han Tae Sul's name, Choi Jae Sun showed her the news on TV.