"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 indulges in death metal karaoke, using the aggressive music as an outlet for her pent-up emotions. This duality—her outwardly polite and reserved demeanor contrasted with her inner rage—forms the core of her character.

The series explores Retsuko's struggles to navigate her professional and personal life. Her boss, Director Ton, is a chauvinistic pig who frequently belittles her, while her colleagues, such as the gossipy Fenneko and the laid-back Haida, add layers of complexity to her workplace dynamics. Haida, a hyena, harbors unspoken feelings for Retsuko, which occasionally surface but are complicated by her indecisiveness and his own insecurities.

As the story progresses, Retsuko faces various challenges, including societal pressures to marry, the pursuit of personal happiness, and the search for meaning beyond her job. She experiments with different paths, such as joining a matchmaking service, pursuing a side hustle as a DJ, and even considering quitting her job. These endeavors often lead to humorous or poignant moments, highlighting the tension between societal expectations and individual desires.

The narrative also delves into the lives of supporting characters, providing a broader view of modern Japanese society. Themes such as gender roles, workplace inequality, and generational differences are explored through their interactions. Despite the comedic tone, the series frequently addresses serious issues, blending satire with relatable, slice-of-life storytelling.

Retsuko's journey is one of self-discovery, as she learns to assert herself, confront her fears, and find balance between her professional obligations and personal aspirations. The series balances humor, emotional depth, and social commentary, making it a compelling exploration of contemporary life.