"Aggretsuko" centers on Retsuko, a 25-year-old red panda working in the accounting department of a Japanese trading firm. Her daily life is marked by the monotony and frustrations of office work, including demanding superiors, tedious tasks, and workplace politics. To cope with her stress, Retsuko secretly channels her emotions through death metal karaoke, a stark contrast to her otherwise reserved and polite demeanor. This duality forms the core of her character, as she navigates the pressures of adulthood while maintaining a facade of compliance in her professional environment.

The series explores Retsuko's relationships with her colleagues, each of whom embodies distinct workplace archetypes. Her boss, Director Ton, is a chauvinistic and overbearing boar who frequently assigns her extra work and belittles her efforts. Her coworker and friend, Fenneko, a fennec fox, provides sharp-witted commentary and often serves as a confidante. Haida, a shy and kind-hearted hyena, harbors romantic feelings for Retsuko but struggles to express them, adding a layer of unspoken tension to their interactions. Other characters, such as the ambitious Tsunoda and the laid-back Komiya, further highlight the dynamics of office life.

As the story progresses, Retsuko faces various challenges, both professional and personal. She grapples with societal expectations, including the pressure to marry and conform to traditional gender roles. Her attempts to find fulfillment outside of work lead to humorous and often poignant situations, such as her forays into online dating, pursuing hobbies, and even considering a career change. The narrative balances comedic moments with deeper themes of self-discovery, resilience, and the search for identity in a rigid corporate culture.

The series also delves into broader social commentary, addressing issues like workplace harassment, generational divides, and the struggles of modern young adults. Retsuko's journey is one of gradual empowerment, as she learns to assert herself and confront the sources of her dissatisfaction. Through its relatable characters and grounded storytelling, "Aggretsuko" offers a candid portrayal of the challenges faced by individuals navigating the complexities of contemporary life.