"Milf Park" centers around a young man named Haruto, who finds himself entangled in an unusual situation after accepting a part-time job at a mysterious amusement park. The park, known as Milf Park, is staffed entirely by mature women, each embodying distinct archetypes and personalities. Haruto's role involves assisting with various tasks around the park, but he quickly discovers that the job is far more complex than he initially anticipated. The women, while professional in their duties, often blur the lines between work and personal interactions, creating a series of comedic and awkward situations.

The narrative explores Haruto's interactions with the staff, including the park's manager, a stern yet caring woman named Aiko, who oversees operations with a no-nonsense attitude. Other key characters include Yumi, a flirtatious and playful ride operator, and Rika, a reserved and intellectual employee who handles the park's logistics. Each episode delves into Haruto's attempts to navigate the challenges of his job while managing the unpredictable dynamics of the staff. The series balances lighthearted humor with moments of character development, as Haruto gradually forms bonds with the women and learns more about their lives outside the park.

The plot progresses through episodic adventures, with each episode focusing on a specific event or challenge at the park, such as preparing for a seasonal festival or addressing a malfunctioning attraction. These scenarios serve as a backdrop for exploring the relationships between Haruto and the staff, as well as the individual backstories of the women. While the tone remains predominantly comedic, there are occasional moments of introspection and emotional depth, particularly as Haruto begins to understand the personal struggles and aspirations of those around him. The series concludes with a sense of resolution, as Haruto reflects on his experiences and the connections he has forged during his time at Milf Park.