The official website for Yo-kai Watch Shadowside: Oni-ō no Fukkatsu (Yo-kai Watch Shadowside: The Return of the Oni King), the fourth film in the Yo-kai Watch franchise, began streaming the film's second trailer on Friday. The video reveals that Mone Kamishiraishi will play Natsume Amano, and Yudai Chiba will play Tōma Tsukinami. The video also shows the new characters, revealing that Natsume is the daughter of Keita. Natsume wields the Yo-kai Watch Elder to fight the Onimaro, and Tōma wields the Kigan Gear to spread evil. The video also reveals the film's antagonist Rasen, the titular Oni King.

In the Yo-kai Watch Shadowside: Oni-ō no Fukkatsu film's story, there used to be a boy who could control yo-kai with a mysterious watch. However, he became unable to see yo-kai when he became an adult. With the boy's duties finished, the watch was buried away in space-time. Then 30 years later, quiet everyday life comes to an end as a fateful day begins with a comet drawing near. The terrible yo-kai virus Onimaro infects people's malevolent intentions and spreads infinitely. The one chosen by the yo-kai watch is the one who can save humanity from its crisis. The bond between humans and yo-kai may be recovered with the attainment of a new yo-kai watch.

The key to the story will be three new human characters. Natsume is a 13-year-old girl who nearly drowned in a river when she was very young. The girl who likes to take care of others remembers "something" saving her from drowning. Tōma is a 13-year-old boy whose parents are busy with work, so he is always alone. Akinori is the oldest son in a family that has used yo-kai in fortune-telling for generations.

LEVEL-5 president and CEO and Yo-kai Watch creator Akihiro Hino is overseeing production of the film, as well as providing the original concept and writing the script. He called the film a "completely new horror comedy" that both children and adults can enjoy. Compared to previous films, the new film will have both scarier and funnier content in addition to intense battles.

New to the film will be the ability for yo-kai to transform into "lightside" and "shadowside" forms. In these forms, yo-kai show different personalities, abilities, and appearances. Jibanyan, Komasan, Whisper, Nurarihyon, Lord Enma, and Slimamander will return in the film.

In addition, the characters from Shigeru Mizuki's GeGeGe no Kitarō manga will appear in the film. Masako Nozawa, who has voiced Kitarō in the manga's numerous anime adaptations, will reprise the role in the film. Shown below (from left to right) are familiar GeGeGe no Kitarō characters Ittan Momen, Medama Oyaji, Konaki Jijii, Sunakake Babaa, Nezumi Otoko, and Neko Musume.

The film will open in Japan on December 16.

Eiga Yo-kai Watch: Sora Tobu Kujira to Double no Sekai no Daibōken da Nyan! (Yo-Kai Watch: The Movie: The Flying Whale and the Grand Adventure of the Double Worlds, Meow!), the third film in the franchise, opened last December. The film topped the Japanese box office and sold 545,211 tickets for 608,033,100 yen (about US$5.189 million) on its opening weekend.