Sasami-san@Ganbaranai centers on Sasami Tsukuyomi, a reclusive high school girl who spends her days confined to her room, observing the outside world through her computer. Her older brother, Kamiomi, takes care of her, though their relationship is strained by his eccentric behavior and mysterious activities. The story takes a surreal turn when Sasami gains the ability to control the world around her through a divine power tied to the Tsukuyomi family, descendants of the moon god. This power manifests in bizarre and often chaotic ways, reshaping reality and drawing the attention of supernatural forces.

The narrative intertwines elements of Japanese mythology, particularly the Shinto pantheon, with modern-day settings. Kamiomi, who serves as a priest at a local shrine, is revealed to be entangled with three goddesses—Tama, Tsurugi, and Kagami—who take on human forms and interact with the siblings. These goddesses are tied to the Tsukuyomi family’s divine lineage and play pivotal roles in the unfolding events. As Sasami’s powers grow, the boundary between the mundane and the divine blurs, leading to increasingly surreal and unpredictable situations.

Themes of family, identity, and the clash between tradition and modernity are explored through the interactions between Sasami, Kamiomi, and the goddesses. The story delves into the complexities of Sasami’s isolation and her struggle to reconcile her human emotions with her divine heritage. The series balances moments of humor and absurdity with darker, more introspective tones, creating a narrative that is both whimsical and thought-provoking. The plot progresses through a series of episodic yet interconnected events, culminating in a resolution that ties together the mythological and personal threads of the story.