Ten years. It has already been ten years since Ji Hyun has been searching for the one who holds the key.

Ji Hyun’s life was filled with pain, bruises, and curses. Because of her abusive parents, the innocent little girl became afraid and fragile. She was forced to live a life that she doesn’t want.

But, just like what she was told before, she continues to follow her own dreams. The boy that she met a long time ago – the owner of the key – was her first friend, her first love.

Back then, promises have been made.

“In the future, when I come back, we’ll be boyfriend and girlfriend, okay?”

Beautiful gifts were given for remembrance.

“When you look at this locket, remember to always follow your own dreams no matter what your parents say… and also… remember me.”

Meaningful words have showed how much they cared for each other.

“Don’t be trapped in someone else’s dream because you’re the only one who controls your own life.”

“Together, we are bulletproof. We will withstand everything that comes into our way no matter what kind of hardship it is.”

But after ten years of not seeing each other, will Ji Hyun be able to recognize him? The little boy that she met the age of five who stood up for her in front of her parents. The one who made her life happier though she gets mistreated by her parents all the time.

He took a hit for her.

“I’m sorry miss but you shouldn’t hit your daughter like that!”

Though, at the time, Ji Hyun didn’t even know he existed but he was determined to protect her.

“I’m her dark knight."