They've known each other for years. He was a constant in her life, the best friend of her brother who had been there since she was a nine year old girl. She was the spoiled little sister of his friend's whose sole purpose of existence was to practice practical jokes on. They grew up together almost like brothers and sisters until tragedy struck and his world turned upside down.

Who knew when friendship grew to be love. Who would have guessed a simple act of kindness in the name of friendship would lead to eternal oath towards each other. They were friends without benefit, whom had grown to develop deeper feelings with time. This is the story of Lee Changsub & Bae Irene of Cool Hot Sweet L.O.V.E.