Everybody under the age of 25 are dying and there is no cure.
Nobody knows why and how to overcome it.
Nobody can overcome death itself.

In this world, there are two people who share the same aura, and with that, they also share the amount of time they will get to live. To live longer than 25 years, each individual must find the person they share their aura with and kill them. That's just how the world works. Nobody knew how it all started, some say it was a disease, others said it was a side-effect from all the nukes used in the Global War that happened in 2044. Anyways, the human body has changed, and  nobody knows how to turn things to the way it was. Scientists are trying different ways to reverse the effect but until then, the only way to survive was to murder.

21 year old Choi Minho lives in this sadistic and inhumane world that the earth has become. He goes to KATB: Korea's Assasination Training Board- where kids from 12 onwards leave school and train how to ... well, assasinate. It is to prepare them for the time where they meet the other person who shares their auras and battle for their lives.

WARNING: SPOILER IN COMMENTS.