Following the collapse of the esteemed Kappa Realm under the Otter Dominion, Prince Keppi forfeits most of his authority and finds himself powerless against the invisible Kapa‑zombies. These undead beings infest the world, engineered by the Otters and born from humanity"s deepest yearnings. With no alternatives, Keppi turns to three youthful companions: Kazuki Yasaka, who must always carry a mysterious box; Enta Jinnai, Kazuki"s childhood confidant; and Tooi Kuji, a rebellious truancy student. By extracting the legendary organ known as shirikodama from each of them, the trio transforms into Kappa and confronts the Kapa‑zombies. Yet to vanquish these foes, they must link their minds, bodies, and—most crucially—guarded truths. As the Kappa Realm depends on them, they must disclose parts of themselves never before revealed, discovering that bonds are delicate yet invaluable.
