In Tokyo, the protagonist "Miseki Ruriiro" hears the voice of a whale. Spreading outside the window, the surface of indigo and white, due to the increasing heat, the voices of the cicadas are fainted. The sky seen form the air-conditioned classroom seems so far away. In the third year. He who is still devoted to his club activities. She who is desperately practicing for an interview to earn a recommendation. Everything is gradually getting further away. In six months, our student lives will come to an end. This is the last―― Blue, season. Knowing that such a summer is approaching, it is frightening. Last summer. Ruriiro was approached by his twin sister "Soubi," inviting him to a movie shoot. Before he could refuse, he found himself filming with two of his classmates whom his sister had gathered. "Because Soubi's special." Ruriiro has always stayed on the sidelines in the shadow of his talented younger sister. However, as he spent time with his shooting buddies "Minamo" and "Nagi," his transparent life began to change. For the first time, experiencing emotions, and numerous struggles. "Even the sky, even the sea. When close to them, they're transparent." The transparent blue enveloped him, in that season, he started to realize. And it was that summer――. ――Soubi disappeared.
