Japan during the Heian period, a time when spirits and yokai lurked just beyond the veil of human perception. Thirteen-year-old Masahiro serves the Imperial Court as a royal diviner and exorcist, a position he inherited from his world-renowned grandfather, the legendary Abe no Seimei. While many would be proud to follow in such esteemed footsteps, Masahiro chafes under the constant comparison, tired of being introduced only as Seimei's grandson and determined to surpass the legendary man.

The young exorcist is aided by his mysterious spirit companion, Mokkun, a creature with a deceptively cute, rabbit-or-fox-like appearance who hides a formidable secret power and often accompanies Masahiro with teasing yet invaluable guidance. The first major conflict arises when Masahiro detects an insidious and ominous presence targeting a young princess within the heavily guarded royal palace. This event serves as his chance to prove his worth and begin his journey out of his grandfathers shadow.

As the series progresses, the narrative expands beyond the initial rescue. Masahiro must balance his duties at court with intense training to master his inherited abilities, complicated by the fact that his grandfather sealed a portion of his immense powers when he was a child to protect him. One notable arc involves the Kikouden Festival, where Masahiro finds his schedule overwhelmed by tracking powerful creatures like the demon Qiongqi while preparing for the celebrations. Simultaneously, he faces a deeply personal threat when Princess Akiko reports a demon lurking outside her chambers each night. Masahiro is compelled to investigate, only to discover that this same demon is mysteriously connected to the frightening nightmares that have plagued his own sleep since childhood, forcing him to confront his past traumas to save the princess. The series is an adaptation of the long-running historical fantasy light novel series Juvenile Onmyogi, bringing a new visual interpretation to Masahiro's supernatural coming-of-age story.