Pesu functions as a companion animal to the central family, characterized by yellow fur, thick eyebrows reminiscent of his caretaker's, a red belt patterned with white dots, and a small triangular nose.

Hagemaru encountered him as a puppy inside a park box during a childhood incident involving wet pants. The boy used the puppy for makeshift cleanup before bringing him to the Hageda residence, establishing their long-term cohabitation.

His behavior blends canine and human-like traits, including vocal capabilities such as speech and singing during films. Loyalty anchors his bond with the family, though he frequently deploys sarcasm regarding their extreme frugality—particularly food scarcity affecting him—and exhibits self-preservation through resource hoarding.

Preferences include consuming shots, experiencing baths, and observing trouser-dropping incidents. He shows affection for Aiko Hageda and Midori across narratives but avoids bone-related items. A complex dynamic with Hagemaru oscillates between rivalry and companionship.

Cinematic narratives expand his experiences: one positions him as Midori's companion, while another depicts temporary ownership under Obochamma. Film conclusions reveal his speaking-capable parents and offspring. Alternate plots reimagine him as Hagemaru's sibling or associate him with entertainment industry roles.

Social connections include friendship with Obochamma Kun, rivalry with Hagemaru, and romantic interest toward Fluffy and Midori across media. His role extends to educational settings via interactions with Masaru Kondo.