During the Meiji era's dawn, a formidable prison, Gokumonjou, emerges in a vast lake to combat escalating crime. The Kumou siblings—Tenka, the unconventional leader; Soramaru, daring yet honorable; and Chuutarou, innocent and youngest—serve as ferrymen. Despite their somber duty, they reside peacefully in the perpetually overcast Oumi with their caretaker, Shirasu Kinjou. In Oumi's ancient lore lies the chilling tale of 'Orochi,' a cyclical menace awakening in a human guise every three centuries. Unaware of their true heritage, Soramaru and Chuutarou must fulfill the Kumou family legacy by subduing Orochi before calamity strikes. As the beast stirs once more, the siblings must find courage to smile through the looming clouds.