Song Yeon Jin (you) loved playing in the playground when you were 6 years old. Just then, you saw a group of boys quarreling against a smaller kid. You ran and tried to fight against them. Seeing you were a girl, they backed and ran away. You helped this little boy named Lee Donghae. He was also 6. He was so ashamed of being helped by a girl. From then on, he had made a promise.

A promise that is still kept until now. 

A promise to take care of Yeon Jin from that time onwards. 

A promise to always be there for her.

A promise to be her Superman...