Irene hates people who lies but

she has an ability.

She could see how many times a person lied.

Numbers would just appear above their heads whenever Irene looked at them.

Thousands, hundreds, tens.

Irene has seen all of those kinds.

But she haven't met single digits. 

Let it alone, 

Zero

But then she met a rare girl with the number zero indicated above her head. 

Both of them got together.

But one day...

Irene found out that Seulgi had lied to her.