Takao, who is training to become a shoemaker, skipped school and is sketching shoes in a Japanese-style garden. He meets a mysterious woman, Yukino, who is older than him. Then, without arranging the times, the two start to see each other again and again, but only on rainy days. They deepen their relationship and open up to each other. But the end of the rainy season soon approaches …

In a post-war alternative timeline, Japan is divided into the North, controlled by the Union, and the South, controlled by the United States. A mysterious high tower rises within the borders of the Union. Three high school students promise to cross the border with a self-built airplane and unravel the secret of the tower.