Ritsu Iijima inherited two things from his late novelist grandfather: the ability to see ghosts and demons, and a powerful demon guardian named Blue Storm. This supernatural inheritance forms the core of Hyakki Yakou Shou, a story that follows Ritsu as he navigates a world where the veil between the living and the spirit world is dangerously thin.

The setting is a contemporary Japan where spirits, yokai, and other beings from folklore quietly exist alongside the everyday, often invisible to ordinary people. Ritsu, now vulnerable after the death of his grandfather who once shielded him, formalizes a contract with Blue Storm, a formidable and loyal demon who becomes his protector. However, Blue Storm's presence seems to attract as many strange occurrences as it resolves. Together, this unlikely pair finds themselves constantly drawn into mysterious events involving the supernatural.

Rather than a single continuous conflict, the narrative unfolds through a series of largely independent episodes. Each story presents a new encounter with a spirit or paranormal phenomenon, ranging from tragic and melancholic to unsettling and eerie. A notable narrative arc involves Ritsu's evolving relationship with his inherited guardian; what begins as a forced pact gradually deepens into a bond of mutual reliance and understanding. Another recurring thread involves Ritsu's family, particularly his cousin Tsukasa Iijima, who becomes entangled in the supernatural events surrounding him. The series explores how different characters deal with things not of this world, from Ritsu's reluctant acceptance to the fear and curiosity of those who glimpse this hidden reality. The tone is less about graphic horror and more focused on mystery, folklore, and the poignant or unsettling consequences of contact with the spiritual realm. Key narrative threads include Ritsu coming to terms with his spiritual heritage, learning that not all spirits are malevolent—some merely seek help or closure—and the persistent challenge of maintaining a normal life while being a magnet for the paranormal. The production, directed by Saya Fukase, is presented in a short-episode format designed to deliver compact, atmospheric ghost stories.