In 2099, Earth has shifted off its axis and begins to rotate at an angle of 90% to the 20th-century equator. Three years of natural disasters follows, and when things settle down, Earth's ten billion population has died and only two million moon colonists remain. Some return to begin the repopulation of the world in seven new cities and the remaining colonists of the moon fear that their former neighbors might pose a threat and construct a ring of defensive satellites to trap them on the newly repopulated homeworld.

In 1945, the second and third-year students of a Hiroshima girls' school are taken away to work in war factories. The remaining 220 girls of the first year try to make the best of their new-found status as the only teenagers in an almost deserted town, even amid the deprivations of wartime. On the 7th of August, an American bomber changes their lives forever. Broadcast on the 43rd anniversary of Hiroshima in memory of "the girls who lost their lives to the atom bomb."

The story follows Risa, a girl with zero experience in romance. Meanwhile, a boy named Yuugure is the most popular student in Risa's school year. Even though the two have had no contact with each other in the past, they find themselves at school at the same time one night.

The day Lee Joon joins Minsong University to reunite with Kim Margo, his high school crush, he is attacked by his new neighbor Lee Duna, a gorgeous former idol. Violent and impulsive, Duna turns Joon's world upside down. Later, to Joon's confusion, Margo seems incapable of making time to meet with him. To add to his dismay, Joon meets fellow student Choi Ira at a party. She becomes enamored with him after the pair partake in a risqué game. As Joon progressively discovers the truth about Duna's troubled past and Margo's harsh family conditions, he tries to sort out his tangled feelings.