The flame that burns twice as bright burns half as long, and so it is with the lives of young shinobi. Death comes swiftly — for the lucky ones — and for those still living, grief is a constant companion. Ryōbi and Ryōna, two shinobi sisters of the Hebijo Clandestine Girls' Academy elite, know that truth all too well, and they mourn their beloved elder sister every day.
But when a mystical phenomenon appears, drawing the shinobi world's finest young ladies into a parallel dimension, everything they know about life and death turns upside down. Taken to a strange world resembling a warm summer island, the girls find themselves face to face with their departed loved ones.
The island's mysterious mistresses challenge the girls, who hail from four different rival schools, to a contest of strength and wits. The winning school, so they promise, will not only learn the highest secrets of shinobi lore, but will also have the honor of laying their loved ones' souls to rest.
The buxom beauties prepare for a new kind of battle, facing not only their rivals, but questions galore. Can the island's hosts be trusted? Will the other schools play fair, team up, or cheat? Will there be time to enjoy the beach before the fighting starts? Will anyone manage to keep their clothes intact? And…if they do win, can they bear to part from their loved ones a second time?