"Happy Mania" is a romantic comedy manga that explores the chaotic love life of Shigeta Takahashi, a young woman in her mid-20s navigating the challenges of relationships, self-worth, and societal expectations. Set in contemporary Japan, the story delves into Shigeta's relentless pursuit of romantic fulfillment, often driven by her impulsive decisions and insecurities. Despite her efforts to find a stable and loving partner, her relationships are frequently marked by dysfunction, misunderstandings, and emotional turmoil.

Shigeta works at a bookstore and lives with her best friend, Mami, who provides a grounded contrast to Shigeta's erratic behavior. Throughout the series, Shigeta becomes involved with several men, each relationship highlighting different aspects of her personality and struggles. Her romantic entanglements include a manipulative coworker, a married man, and a younger, more carefree partner, among others. These relationships often spiral into dramatic and comedic situations, revealing Shigeta's vulnerability and her tendency to prioritize romantic validation over self-respect.

The narrative balances humor with poignant moments, portraying Shigeta's growth as she confronts her flaws and learns to value herself independently of her romantic pursuits. The supporting characters, including Mami and Shigeta's various love interests, add depth to the story, offering perspectives on love, friendship, and personal growth. The manga's episodic structure allows for a detailed exploration of Shigeta's journey, blending lighthearted comedy with themes of self-discovery and the complexities of modern relationships.