The title of the film comes from a Japanese proverb: "A fool is as foolish to pluck a sakura as he is not to pluck a plum". The proverb reminds us that each thing has its own specific characteristics to adapt to - the branches of the sakura begin to rot when pruned, and the blossom and fruit of the plum blossom will turn brown if the branches are not pruned. In addition to filmmaking, director K. Wajima has since 2017 been broadcasting an online show called "Listening to Epilepsy: Potsu Radio", featuring guest appearances by people with epilepsy or their family members.

The Untended Plum Tree tells the story of Tamako (Mariko Kaga) and her 50-year-old son Tadao (Muga Tsukaji), who has autism. Their neighbours resent Tadao's unpredictable behaviour and also complain about the branch of a plum tree sticking out of the fence. One day, Tamako learns of a vacancy in a group home for people with disabilities and decides to send her son there. She hopes that Tadao will be able to live more independently, but he runs away, bewildered by the sudden change in his surroundings.