Mononoke follows a wandering, nameless character known only as the "Medicine Seller" (voiced by Takahiro Sakurai in the 2007 series and by Hiroshi Kamiya from 2024 onwards).

The Medicine Seller always proceeds in the same manner, using his knowledge of the supernatural to fend off the mononoke until he can learn the spirit's shape (Katachi), truth (Makoto), and reasoning (Kotowari).

At this point, realizing their wish would only cause harm to the only person who showed them kindness, the Zashiki Warashi smiles and allows the Medicine Seller to destroy them with the sword.

Traveling on a merchant's luxurious ship, the Medicine Seller and the other passengers drift into the Dragon's Triangle, a mysterious sea full of ayakashi.

Among the passengers are Kayo, a servant girl from the Sakai house of Bakeneko fame; Genkei, a Buddhist monk; and Genyousai, a minstrel and spiritualist.

Through the appearance of Umizatou, an ayakashi who demands that the passengers reveal their worst fears, the group discovers that Genkei was the one who set the ship off course.

Upon hearing this, the young, recently promoted monk fled, vowing to commit suicide to join Oyō in the afterlife.

He could not do this and, instead, spent 50 years in deep meditation praying for the soul of his poor sister Oyō, her corpse supposedly adrift in the hollow boat in the Ayakashi Sea.

Tragically, the ayakashi showed the hollow boat to the current passengers by dragging it up from the bottom of the sea onto the deck of their ship.

Although they thought they heard scratching from the inside, they discovered that it had lain empty for 50 years and that Oyō had in reality "given herself to the sea", as she too could no longer live with her own lust for her brother.

A despairing woman named Ochou, wishing for freedom but unable to escape her oppression, confesses to killing her husband's entire family.

This chapter makes a reference to the Rannatai (the type of wood described above) that once existed in the Shōsōin (Great Treasure Room) of the Tōdai-ji temple in Nara, Japan.

The medicine seller questions the passengers to reveal a dark connection between them, shedding light on the murder of a young newspaper reporter.

At the end of the episode, the woman's spirit has its revenge, the passengers are saved, and the medicine seller challenges the audience to reveal to him their truth and reason, vowing to continue hunting mononoke as long as they roam the world.

[7][8] The film, titled Mononoke the Movie: Phantom in the Rain, was released on July 26, 2024, with Hiroshi Kamiya performing the role of the Medicine Seller.

[21][22] A manga adaptation of the Mononoke the Movie: Phantom in the Rain film began serialization in Kodansha's Monthly Shōnen Sirius magazine on May 26, 2024.

[25] It blends a murder mystery structure with a "twist of supernatural and a shake of historical, peppered with plenty of stylistic experimentation".

[25] The Mainichi Shimbun newspaper said it could not be dismissed as a mere experiment and that the story's themes were every bit as advanced as the digital animation techniques employed.