Haru is a male Shiba Inu known for his cheerful demeanor and inclination for philosophical discussions, frequently citing concepts such as Schrödinger's cat or Occam's razor. He journeys with the last surviving human, whom he steadfastly calls "Master," exhibiting deep loyalty and prioritizing her companionship above all else. His personality blends self-assured intelligence with moments of factual inaccuracy, especially during conversations where he confidently imparts incorrect details.

Haru interacts with diverse post-apocalyptic entities, including mythological creatures and extraterrestrial beings, while adhering to a distinctly canine social dynamic. He engages in breed-based comparisons, particularly between Western and Japanese dogs, and navigates romantic interest from female Shiba Inus like Snow White, subtly establishing a social hierarchy among surviving animals. His expressions often incorporate visual humor reminiscent of "doge" internet memes, introducing levity.

His background includes initial adoption from a pet shop, shown in a bonus story depicting his first meeting with his owner. This origin story contextualizes their bond and offers glimpses into his owner's pre-apocalypse family life. His development consistently highlights protective instincts, notably when he orchestrates her rescue after imprisonment by canine-liberating aliens.

Haru's role transcends companionship; he actively engages the transformed world through observational commentary on environmental shifts and encounters with other surviving species. His journey focuses on episodic adventures rather than continuous plot, with his relationship to his owner serving as the constant narrative thread across all media.