Release date: September 29, 2026 on Netflix

Directed by Tomoaki Koshida.

Written by Yasumi Atarashi.

Original Score by Taku Iwasaki.

Synopsis: After the fierce battle between the Medicine Seller, wielder of the Sacred Sword, and the Karakasa, followed by the conflict with the Hinezumi — two major incidents born of Mononoke — peace appears, at last, to have returned to the Inner Chambers. Yet the Medicine Seller senses that something has not been laid to rest… and remains ever watchful.

Amidst this uneasy calm, Yukiko, the lawful wife of the Emperor, is blessed with a long-awaited male heir. But the joy is fleeting — the child is lost, despite all prayers offered.

Having wished to change her hollow marriage through the birth of an heir, Yukiko falls into despair… and is drawn into a conspiracy that threatens the very foundation of the Inner Chambers.

Grief without salvation. Rage without refuge. Such emotions begin to take shape. Hokuto Mizorogi, priest of the Inner Chambers’ faith known as “Omizusama,” watches in silence. At the same time, unnatural tremors begin to shake the Inner Chambers. As though something vast crawls beneath the earth, triangular scales drift down from nowhere… and soon, a series of grotesque deaths follows, bodies twisted, crushed, and strangled.

Before the Medicine Seller appears a Mononoke in the form of a great serpent, the snake god. Though it is temporarily driven back with talismans, the Medicine Seller cannot draw the Sacred Sword. To do so, he must uncover its “Shape”, “Truth”, and “Reason”. Only then can the sword be unsheathed, and the Mononoke cut down.

Where was the snake god born? Why does it harbor such overwhelming rage? And why has it risen now?

The answers lie 150 years in the past, in the hidden truth behind the creation of the Ooku. Long ago, the Inner Chambers were established by Ama-no-Tsubone, wet nurse to the Third Emperor.

Its system sustained an era of peace, and in time came to be revered as “Omizusama”. Sensing a growing disturbance, the Medicine Seller makes his way to the shrine at the heart of the altar, and there, uncovers a truth that was never meant to be spoken.

The tangled fate between the third lawful wife and Ama-no-Tsubone, the secrets of the Mizorogi family, and the true reason behind the successive appearances of Mononoke in the Ooku all come to light, connecting every thread into one.

Facing what can only be described as the embodiment of the Ooku’s dark history, the Medicine Seller prepares to stake everything in battle. But the snake god, empowered by centuries of accumulated hatred, possesses unimaginable strength, pushing him into an unprecedented crisis. As death closes in, even more unpredictable horrors unfold.

What fate awaits the Medicine Seller as he faces his greatest trial yet?

Japanese voice cast:
Hiroshi Kamiya as Medicine Seller
Atsumi Tanezaki as Yukiko
Miyu Irino as Tenshi
Kenjiro Tsuda as Hokuto Mizorogi
Yoshiko Sakakibara as Suikoin
Tomoyo Kurosawa as Asa
Yoko Hikasa as Fuki Tokita
Haruka Tomatsu as Botan Otomo
Yuki Kaji as Saburomaru Tokita
Jun Fukuyama as Hiramoto Saga
Daisuke Hosomi as Sakashita
Cho as Yoshimichi Tokita
Ryo Horikawa as Fujimaki
Yukana as Amanotsubone
Fumi Hirano as Tokiwai
Mariko Honda as Kawa
Eiji Takemoto as Saku Mizorogi
Miyuki Sawashiro as Third Midaidokoro