Boundary Realm lies on the opposite bank of Lethe River, where ghost messengers work tirelessly during the nocturnal hours to maintain the equilibrium of the world's deaths. The Black and White Warriors are among the messengers, tasked with collecting spirits from the Human Realm. Among them are Xiaohei and Xiaobai, whose once strong bond is now fragile following a troubling event in the One Hundred Ghost Great Seal. Meanwhile, Xiaobai's true identity is beginning to be revealed.