Harunobu Madarame is a central figure known for being one of the most hardcore and devoted otaku within the group. Physically, he is tall with broad shoulders, though his build is often described as frail, a consequence of a poor diet that results from spending the majority of his money on doujinshi and merchandise. He has shallow eyes and is frequently depicted with small, prominent fangs visible at the corners of his mouth. His typical attire is cheap and functional, common for a fan, though he adopts a more fashionable jacket and suit at the encouragement of Saki Kasukabe, which he later dubs his battle wear for shopping trips to Akihabara.

Madarame takes immense pride in his lifestyle to the point where the official data book for the series labels the highest level of otaku as Madarame. He is an aficionado of Gundam and specializes in anime, manga trivia, and dating sims, including adult games. In conversations, he enjoys quizzing others and pointing out inconsistencies in their knowledge. Despite his pride, he is generally a coward when facing real-world adversity, often avoiding confrontation or physical danger. However, he is capable of taking a bold stand when his principles or the club itself are threatened, even if doing so makes him extremely nervous.

His motivations are largely driven by a genuine, all-consuming passion for his hobbies, prioritizing the acquisition of collectibles over basic necessities like food. One of his most significant internal motivations is a closely guarded secret: he gradually falls in love with Saki Kasukabe. Despite their frequently antagonistic relationship, where he is often the recipient of her physical aggression, he never confesses his feelings, convinced they have no chance of being reciprocated. A specific traumatic event from his high school years, where an insensitive remark led to public humiliation and a year of social isolation, profoundly affects his interactions with women and explains much of his avoidance of romantic vulnerability.

Within the story, Madarame serves as a veteran and a benchmark for otaku culture. Although not the founder, he is personally appointed as the second president of the club, showing more leadership and initiative than others before his formal appointment. He acts as a mentor to newer members like Kanji Sasahara, though his leadership style is contradictory; he drives cultural initiatives but often delegates administrative duties. After graduating, he secures a desk job at a nearby sewage construction facility, leveraging his computer literacy gained from playing porn games. He continues to frequently visit the clubroom, maintaining his ties to the university and its members. In the later arcs, he plays a key role in helping a new member, Kenjirou Hato, by allowing him to use his apartment to change clothes, a practical show of support.

Key relationships define much of his story. His unspoken affection for Saki remains a central, unresolved tension for many years, though they eventually become good friends. He shares a deep camaraderie with his fellow club members, including Makoto Kousaka, Tanaka, and Sasahara. He endures the persistent misnomer of Watanabe from Keiko Sasahara, a joke at the expense of his unusual name. In the sequel series, he inadvertently becomes the focal point of romantic attention from multiple characters, including Angela, Sue, Keiko, and Hato, though he remains oblivious to most of it until directly confronted. A later relationship with Sue represents a sign of tentative emotional growth.

Throughout the series, Madarame exhibits subtle but noticeable development. He transitions from a financially reckless student who breaks bones from malnutrition and refuses to leave a convention before buying his desired goods, to a working adult with a stable job. He shows nascent maturity by improving his cooking skills and wistfully acknowledging the fading of his obsessions as he ages. His notable abilities include his encyclopedic knowledge of otaku media and his surprisingly high computer literacy, which directly leads to his employment. Perhaps his defining ability is his unyielding pride in being an otaku, a trait that allows him to wear his lifestyle on his sleeve and, in turn, inspires others to be more confident in their own identities as fans.