"Nyanko Days" is a short-form anime series that centers around the daily life of a shy high school girl named Maasa and her interactions with three tiny, anthropomorphic cats who live with her. The cats—Roku, Shii, and Nagi—each have distinct personalities and appearances. Roku is a black cat with a calm and mature demeanor, Shii is a white cat who is energetic and playful, and Nagi is a gray cat with a reserved and somewhat aloof attitude. Despite their small size, the cats behave like humans, walking on two legs and engaging in activities such as cooking, cleaning, and even playing video games.

The narrative unfolds through a series of lighthearted, slice-of-life vignettes that highlight the bond between Maasa and her feline companions. Maasa, who struggles with social anxiety, finds comfort and companionship in the cats, who often encourage her to step out of her comfort zone. The cats also interact with Maasa’s classmate, Azumi, who is outgoing and friendly, further bridging the gap between Maasa and the outside world. The series emphasizes themes of friendship, personal growth, and the joy of small, everyday moments.

The episodic structure of "Nyanko Days" focuses on the cats’ antics and their efforts to support Maasa, often resulting in humorous and heartwarming situations. The cats’ human-like behavior and their ability to communicate with Maasa add a whimsical element to the story, while their small size and adorable designs contribute to the series’ charm. The narrative remains grounded in its portrayal of Maasa’s gradual development as she learns to navigate her social anxieties with the help of her feline friends. The series balances its comedic and emotional tones, creating a gentle and endearing viewing experience.