During the Edo period, Ichitarou, the sickly heir of a well-known pharmacy, spends most of his time confined to his room because of his fragile health. Unfavorable gossip surrounds his condition, leading his grandfather to pray for protective spirits. In response, two guardians named Sasuke and Nikichi are assigned to watch over Ichitarou throughout his life, ensuring his safety and well-being.
As Ichitarou grows older, he increasingly wishes to do something beyond his room, despite being advised by others to rest. One evening, he sneaks out alone without his guardians and remains outside after sunset. On his way back, he meets a bleeding person who pursues him. Using quick thinking, Ichitarou escapes and ends up at the scene of a brutal murder.
The next day, news of the killing spreads, but the reported description of the victim's wound does not match what Ichitarou witnessed. With the culprit still at large, Ichitarou decides to investigate further, gathering information from both human and supernatural sources, hoping to solve the mystery.