"Aggressive Retsuko" 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 bosses, tedious tasks, and workplace politics. To cope with her stress, Retsuko channels her emotions into death metal karaoke sessions, where she vents her frustrations through aggressive singing. This duality—her meek, polite demeanor at work versus her explosive, cathartic outbursts in private—forms the core of her character.

The narrative explores Retsuko's struggles with societal expectations, gender roles, and the pressures of adulthood. Her interactions with colleagues, such as the domineering Director Ton, the gossipy Fenneko, and the laid-back Haida, highlight the dynamics of workplace relationships. Haida, a hyena and fellow coworker, harbors unspoken feelings for Retsuko, adding a layer of romantic tension to the story. However, Retsuko's focus remains on navigating her career and personal growth rather than pursuing romance.

As the series progresses, Retsuko faces various challenges, including job dissatisfaction, financial struggles, and societal pressures to marry. Her journey involves exploring alternative paths to happiness, such as pursuing hobbies, forming friendships, and questioning the traditional trajectory of life. The story balances humor and relatability, using anthropomorphic animal characters to reflect universal themes of modern adulthood, resilience, and self-discovery. Through its episodic structure, "Aggressive Retsuko" offers a candid portrayal of the complexities of balancing personal aspirations with societal expectations.