A salaryman in his 30s with a wife and a daughter. Kim Yoon Seong was a man with a perfect life: a job, a loving wife, and a daughter. All this changes when one day he turns into a Trace with powerful legs. Being a law-abiding citizen, he decides to legally register as a trace, rather than hide his identity.
After that he is separated from his family who are taken to a trace facility where the family of the traces are taken.When he is not able to contact them he goes to the facility to see his family where he is stopped by a group of trace guards and chased where he meets Jeong Hee Sub who is also a trace trying to get into the facility. They join and form a team and recruit other members. They succeed in entering the facility where Kim Yun Seong finds the family of the traces who are brought there are used for experimental purposes and killed.
Note: Tsukishiro Kai (月城カイ) is the name used in an alternate Japanese version/rewrite.