"Baka-Kyōdai" centers on the lives of two brothers, Haruo and Naoto, who share a strained yet deeply intertwined relationship. Haruo, the older brother, is a 40-year-old unemployed man with a penchant for gambling and a carefree, irresponsible attitude. Despite his flaws, he harbors a deep sense of loyalty and love for his younger brother, Naoto, who is a successful and disciplined professional. Naoto, in contrast, is a 32-year-old salaryman who has worked hard to distance himself from his brother’s chaotic lifestyle, yet he remains tethered to Haruo by a mix of obligation and unresolved familial bonds.

The narrative unfolds through a series of episodic events that highlight the brothers’ contrasting personalities and the challenges they face individually and together. Haruo’s reckless behavior often leads to financial and emotional crises, forcing Naoto to step in and clean up the mess. Despite Naoto’s frustration with Haruo’s immaturity, he frequently finds himself drawn back into his brother’s orbit, revealing a complex dynamic of resentment, dependence, and unspoken affection. The story explores themes of family, responsibility, and the enduring ties that bind siblings, even in the face of personal failures and societal expectations.

Supporting characters, such as Haruo’s gambling acquaintances and Naoto’s colleagues, add depth to the narrative, providing context for the brothers’ struggles and occasional moments of levity. The manga balances humor with poignant moments, capturing the absurdity and heartache of their relationship. Through its portrayal of flawed yet relatable characters, "Baka-Kyōdai" offers a nuanced exploration of brotherhood, resilience, and the ways in which family shapes identity.