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 Y