"Mayoi Neko Overrun!" centers around Takumi Tsuzuki, a high school student who lives and works at Stray Cats, a struggling confectionery shop run by his older sister, Otome. The shop also serves as a home for several other individuals, creating a lively and chaotic environment. One day, Takumi encounters a lost girl named Nozomi Kiriya, who is searching for her brother. After learning she has nowhere to go, Takumi brings her to Stray Cats, where she begins living alongside the other residents.

The story expands as Nozomi integrates into the household, which includes Fumino Serizawa, a sharp-tongued but caring classmate of Takumi, and Chise Umenomori, a wealthy and eccentric girl who frequently visits the shop. The dynamics between the characters drive much of the narrative, with Nozomi’s presence often sparking humorous and heartwarming situations. The group navigates daily life, balancing school, work, and their personal relationships, while also dealing with the challenges of running the struggling confectionery shop.

As the series progresses, the characters’ backstories are gradually revealed, adding depth to their interactions. Nozomi’s search for her brother becomes a recurring subplot, intertwining with the larger narrative of the group’s efforts to keep Stray Cats afloat. The series blends comedy, slice-of-life elements, and occasional moments of drama, creating a lighthearted yet engaging atmosphere. The interactions between Takumi, Nozomi, Fumino, and Chise form the core of the story, with each character contributing to the overall charm and humor of the series.