"Mayoi Neko Overrun!" is a manga series that revolves around Takumi Tsuzuki, a high school student who lives and works at Stray Cats, a small confectionery shop run by his older sister, Otome. The shop also serves as a home for stray cats and people in need. Takumi's life takes a turn when a mysterious girl named Nozomi Kiriya appears, claiming to be the daughter of Otome's estranged friend. Nozomi moves into Stray Cats, bringing chaos and unpredictability to Takumi's daily routine.

The narrative expands with the introduction of Fumino Serizawa, a wealthy and domineering classmate of Takumi who harbors feelings for him. Fumino frequently visits Stray Cats, often clashing with Nozomi due to their contrasting personalities. Another key character is Chise Umenomori, a shy and reserved girl who works part-time at the shop. Chise's quiet demeanor contrasts with the more energetic and assertive personalities of Nozomi and Fumino, creating a dynamic interplay among the characters.

The story explores themes of family, friendship, and belonging, as the characters navigate their relationships and personal struggles. Nozomi's presence at Stray Cats forces Takumi to confront his feelings about responsibility and connection, while Fumino's attempts to win his affection add a layer of romantic tension. Chise's gradual opening up to the group highlights the importance of trust and support in overcoming personal insecurities.

Throughout the series, the characters' interactions are punctuated by comedic moments and lighthearted situations, often involving the stray cats that give the shop its name. The cats serve as a metaphor for the characters themselves, each searching for a place to belong. The narrative balances humor with moments of introspection, creating a story that is both entertaining and emotionally resonant.

The manga's episodic structure allows for a focus on individual character development while maintaining an overarching narrative about the bonds formed at Stray Cats. The relationships between Takumi, Nozomi, Fumino, and Chise evolve over time, with each character contributing to the growth and stability of the makeshift family they create together. The series concludes with a sense of closure, as the characters find their place within the world of Stray Cats and with each other.