An Na Suh lives with her gorgeous brother, Aaron suh (guy up there) who's popular with everyone—regardless of gender. An Na's mother has gone to Africa for a volunteer project and her father has gone missing ever since the day Aaron was brought to the house. Then, one morning, An Na decides to look for her father, and whether it be luck or coincidence, she gets a phone call from the police saying that they've found something related to her father. It turns out that it's a young boy who although looks to be in his teens, acts very child-like. Grasping onto the possibility that the boy could being a clue to finding her father, An Na takes him home. Besides the unknown origins of this boy, the story throws in another puzzle. An Na and Aaron... may not be related! Unfortunately, without the DNA of An Na's father, it is virtually impossible to determine whether or not they are brother and sister. An Na remembers her father asking her if she wanted to go to the moon: "Let's go to the moon