"Hoshi Neko Fullhouse" centers on the life of a young girl named Rinko, who inherits a mysterious old house from her late grandmother. The house, known as Fullhouse, is no ordinary residence—it is inhabited by a group of anthropomorphic cats, each with unique personalities and abilities. These cats, led by the wise and enigmatic leader Shiro, are not mere pets but guardians of a celestial secret tied to the stars. Rinko discovers that her grandmother was part of a lineage tasked with protecting the balance between the human world and the celestial realm, a duty now passed down to her.

As Rinko settles into Fullhouse, she learns that the cats are connected to a constellation that grants them magical powers. Each cat represents a star, and their collective energy maintains harmony between the two worlds. However, this balance is threatened by an ancient force seeking to exploit the constellation's power for its own gain. Rinko, alongside the cats, must navigate a series of challenges to protect the constellation and prevent the collapse of both realms.

The narrative unfolds through episodic adventures, blending slice-of-life moments with supernatural elements. Rinko grows closer to the cats, forming bonds that highlight themes of friendship, responsibility, and self-discovery. Key characters include Shiro, the calm and strategic leader; Kuro, a mischievous yet loyal cat with a knack for problem-solving; and Mikan, a shy but kind-hearted feline who often provides emotional support. Together, they face adversaries ranging from rogue celestial beings to humans who seek to misuse the constellation's power.

The story gradually reveals the history of Fullhouse and its connection to the stars, intertwining Rinko's personal journey with the larger cosmic conflict. As she learns to harness her own latent abilities, Rinko becomes an integral part of the guardianship, ensuring the legacy of her grandmother and the safety of both worlds. The series balances lighthearted moments with deeper emotional undertones, creating a narrative that appeals to a wide audience while maintaining a focus on its central themes.