After its premiere in Japanese theaters in January, Gold Kingdom and Water Kingdom will feature a special pre-recorded talk in screenings of the anime film with voice cast members Kento Kaku and Minami Hamabe, as well as director Kotono Watanabe (Btooom!). 

The announcement is accompanied by a new visual featuring protagonists Sara and Naranbayar, voiced by Hamabe and Kaku respectively. Other voice actors in the film include Hiroshi Kamiya as Saladin, Miyuki Sawashiro as Lailala, Subaru Kimura as Jauhala, Keiko Toda as Leopoldine, Chafurin as Piripappa, Masaki Terasoma as Oodouni, and Banjou Ginga as Rastaban the Third.

Besides Watanabe, the production staff consists of Fumi Tsubota (Waccha PriMagi! and Hugtto! Pretty Cure series screenwriter) as scriptwriter, Mitsuyuki Masuhara (Ace of Diamond and Shirokuma Cafe director) as animation supervisor, and Evan Call (Violet Evergarden) as music composer. Madhouse is handling the animation production for the film. 

The film is based on the manga Kin no Kuni Mizu no Kuni by Nao Iwamoto, which ran in Shogakukan’s monthly Flowers magazine from October 28, 2014 to April 28, 2016. A single tankoubon volume has been released under the Flower Comics label. 

The Animation is Film festival describes the story of Gold Kingdom and Water Kingdom as:

The Gold Kingdom and the Water Kingdom had a long, troubled history filled with epic battles before they decided to take the drastic steps of building a wall between the two lands. But 100 years later, they make good on an agreement in hopes of bringing stability to all. The rulers from each land had decided that the Gold Kingdom would offer the most beautiful girl in their kingdom as a bride, to be wed to the most clever man from the Water Kingdom, creating not just a couple but the promise of renewed relations and peace.

When it comes time for the rulers to make good on their promise, neither is entirely honest or admirable in their attempts. The Gold Kingdom offers Sara, a kind-hearted, but homely princess while the Water Kingdom marries off Naranbayar, a lanky scholar of modest background. To add insult to injury, the two separately find themselves with a dog (for Sara) and a cat (for Naranbayar) as their partner-to-be. As Sara and Naranbayar individually navigate the palace schemes of their respective homelands, their paths soon converge in a heartwarming new spin on the classic fairytale set-up.

Source: Gold Kingdom and Water Kingdom Official Anime Twitter