Kurt is a small white dog with distinctive black or brown ears, originally named Spank in the Japanese version. His background involves waiting daily at the beach after his owner disappeared at sea, mirroring the loss experienced by his eventual human companion, Anna Martens. Anna, a junior high school student, had recently lost her own dog in a car accident, leaving her devastated. Kurt's persistent presence and clumsy yet endearing nature gradually helped alleviate her grief, leading to their mutual adoption.

Kurt exhibits anthropomorphic behaviors atypical for a dog, including walking on two legs, using utensils to eat, occasionally wearing clothes, and communicating through expressive baby talk. His personality is defined by a merry, big-hearted, and clumsy disposition, often causing unintentional disruptions to the plans of humans and other animals. He forms a close, protective bond with Baron, a smaller dog who looks up to him, and develops a friendly rivalry with Torakichi, a cat. Both compete for the affection of Cat, a female Siamese cat owned by Anna's classmate Celine.

Kurt's romantic pursuits are a recurring aspect of his character. He harbors a persistent, mostly unrequited crush on Cat, who shares her owner's snobbish demeanor but occasionally shows him kindness. However, his affections shift later in the story when he meets and ultimately forms a relationship with Fan Fan, a female blue dog. This transition resolves his earlier romantic conflicts.

In terms of development, Kurt evolves from a lonely stray to an integral part of Anna's life, helping her heal from her losses while navigating his own friendships and rivalries. His gluttonous tendencies and impulsive actions frequently create comedic or chaotic situations, yet his unwavering loyalty and optimism consistently mend relationships. The character's growth culminates in emotional stability through his bond with Fan Fan and his enduring role as Anna's companion.