While searching for Nyanko-sensei, Takashi Natsume encounters a small and meek youkai named Mitsumi. Mitsumi was entrusted by Gantetsu, a powerful ayakashi leader, to wake him from his deep slumber as the "Ishi Okoshi." Seeing how much Mitsumi wants to prove himself worthy of Gantetsus service, Natsume decides to help him fulfill this task. However, time is running out because they are not alone in their quest to awaken the divine being.
On another day, Natsumes friend Kaname Tanuma is visited by a strange man who briefly talks with him and then leaves. Natsume soon discovers that the stranger is actually a youkai disguised as a human, claiming to pose no danger. Despite trusting the youkai, Tanumas health begins to deteriorate, causing Natsume to become more suspicious of the interloper's true intentions. What is the truth behind his sudden appearance and his connection with Tanuma?
Natsume Yuujinchou: Ishi Okoshi to Ayashiki Raihousha was released on Blu-ray and DVD on May 26, 2021 in Japan.