"Monster", that's what he thought she was. 

Hoya was in love with his classmate. They've been together for 3 years until one day he had to break up with her due to a love triangle they were caught in. And the third party, was you. 

You were a decent girl, loved by friends around her. Each time you see Hoya, your heart starts to beat fast. Having a crush on him from the first time you saw him was hard since he had a girlfriend but you couldn't help but feel sad and alone whenever they are together.