One day, Minakami Yuki witnesses a stuffed toy falling through the air. Battered and worn, how many times has this doll fluttered downwards, released as an attempted offering to the sky? An offering made to find the "day we return to the sky"—a ritual passed down in this town since times gone by. Those efforts shall come to fruition in the place where the girls of earth and sky meet. Vega and Altair—Orihime and Hikoboshi—two points of light separated by the vast Milky Way. Together with Deneb, crown of the Northern Cross, they make up the Summer Triangle. Evoking the concept of the Trinity, this formation is also known as the "Heavenly Triangle." When this Heavenly Triangle shines overhead, the world and the sky will meet. Takashima Zakuro, Wakatsuki Kagami, Wakatsuki Tsukasa, and our heroine, Minakami Yuki, set off in search of that place where the points of the divine triangle cross—where world and sky join together.