Happiness Bunny is a stuffed rabbit toy belonging to Nene Sakurada, one of the main kindergarten friends in the series. The toy is a simple, plush bunny that serves as a recurring visual gag and a vessel for a darker, recurring storyline. In its primary role, the bunny is an inanimate object that Nene and her mother use as a physical outlet for their frustration and anger. When either of them becomes stressed or furious, commonly due to the antics of the main character Shin, they grab the Happiness Bunny and repeatedly punch it, using it as a surrogate to vent their emotions. This habit is explicitly identified as a behavior Nene learned directly from her mother.

Beyond its function as a punching bag, the Happiness Bunny is the focus of a surreal and horror-tinged subplot. In certain episodes, the stuffed animal is depicted as coming to life, typically under the light of a red moon. In this animated state, the Happiness Bunny has a terrifying appearance, characterized by glowing red eyes and a sinister, menacing expression. Its personality becomes vengeful and cruel, seeking retribution against Nene and her mother for the years of physical abuse they have inflicted upon it. The living bunny's motivations are driven by this accumulated pain, as it desires to make its owners pay for treating it poorly. In one instance, after coming to life, it demands that Nene and her mother become its slaves as a form of compensation.

The role of the Happiness Bunny in the story is therefore twofold. It is primarily a comedic device that visually represents the often-hidden explosive anger of Nene and her mother in a way that is absurd and exaggerated. Secondarily, it becomes the central antagonist in a nightmare-like sequence or dream, turning the show's tone from lighthearted comedy to psychological horror. The key relationship for the bunny is with Nene and her mother, as their abuser and, in its living form, as their would-be tormentor. It also has a notable interaction with Shiro, Shinchan's dog; in one episode while animated, it engages in a conversation with the dog about its plight and existence. There is no significant development for the bunny as a persistent character, as its living appearances are episodic and dreamlike, often resetting to its status as an inanimate toy by the episode's end. Its only notable ability, beyond being a durable plush toy, is its capacity to intermittently and mysteriously come to life with malevolent intent and supernatural presence.