Born from the creativity of Amanda's luminous mind, Rudger is an imaginary friend that she alone can hear or see. Together, they go on wild adventures in the attic above the bookshop owned by Amanda's mother. The two have pledged to follow three rules: never disappear, always protect one another, and never cry.

One day, a suspicious man named Mr. Bunting knocks on the door, accompanied by an eerie girl that only Rudger and Amanda can see. He has a keen nose for hunting imaginary friends and depriving children of their precious companions.

During one of Mr. Bunting's failed attempts to capture Rudger, Amanda gets into a fatal car accident. All alone now, Rudger must protect himself from not only his pursuer but also another peril: if an imaginary friend is forgotten, they will completely disappear from existence.

Yaneura no Rudger is an adaptation of the 2014 British children's novel The Imaginary, written by A.F. Harrold and illustrated by Emily Gravett. Through a collaboration between Studio Ponoc and French studio Les Films du Poisson Rouge, the movie combines traditional hand-drawing with new digital techniques.

The film was released on Blu-ray and DVD in Japan by The Walt Disney Studios on May 15, 2024. It premiered internationally as The Imaginary at the Annecy International Animation Film Festival on June 14, 2024. The movie became available worldwide on Netflix, starting July 5, 2024.