Do Kyungsoo was ten when he was first exposed to the criminal world.

He was eleven when his parents were killed by drug addicts.

He was twelve when his sister got and murdered in a night club when she was graduating from high school.

He was thirteen when his brother joined the mafia.

Do Kyungsoo's whole family were taken away by the criminals.

Yet none of the bad guys were caught.

And Kyungsoo ended up being alone. 

No one to rely on.

Believing that the police would be able to catch those people and put them behind bars.

They never did.

He was fifteen when he decided he had enough of the nation's criminal justice system .

Do Kyungsoo ended up joining the CIA at the age of sixteen, with an IQ of 158.

He became an excellent agent at the end of the year.

But when you have the brains and skills.

You tend to not have the heart.

So really, the genius Do Kyungsoo.

Couldn't find the x.

To the equation where a doe-eyed girl had factorised his whole heart.