Mitsunori Kugayama is a college student and a founding member of the Genshiken, the Society for the Study of Modern Visual Culture at Shiiou University. He stands out among his peers for his heavyset build and his persistent stutter, which becomes more pronounced whenever he interacts with people outside his familiar club circle. Despite his outward timidity, Kugayama is the club's primary artist before the arrival of Chika Ogiue, and he adopts the pen name KODAMA for his creative work. However, he struggles with a lack of sustained motivation and commitment, often failing to complete a full doujinshi on his own initiative. His artistic talent is genuine but only surfaces reliably when he is strongly motivated, particularly by erotic subject matter. He is especially skilled at drawing explicit imagery of the character Yamada from the fictional series Kujibiki Unbalance, a focus that seems to unlock his creative drive.

Initially, Kugayama's role within the Genshiken is that of the quiet, capable artist who contributes to the club's activities but rarely pushes himself. When Sasahara becomes club president and asks Kugayama to draw a doujinshi for the Comic-Fest event, Kugayama repeatedly fails to deliver. It takes the forceful intervention of Saki Kasukabe, who pressures him into joining a tight production schedule alongside Sasahara and Ogiue, to finally produce a finished work. Saki also bestows upon him the nickname Kugapii, which sticks throughout the series. Kugayama's personal preferences lean toward lighthearted, family-friendly anime such as Fun with the Tarurun Family, though his artistic output reveals a different side. His favorite manga is Anman Dama, and his favorite game is Exitge.

As the series progresses, Kugayama graduates from university and enters the workforce at a medical device manufacturing company in Iidabashi. His transition into adult professional life marks the end of his active participation in the Genshiken, though his time in the club helped him develop as an artist, even if his motivation remained conditional. He is not a central protagonist, but his presence underscores the theme of latent talent held back by personal inhibitions—a contrast to other members who are more openly passionate or driven. His key relationships within the club include a working dynamic with Sasahara, who tries to push him artistically, and a teasing but effective rapport with Saki, who manages to extract his best work through blunt pressure. After Ogiue joins, Kugayama is no longer the sole artist, and his role gradually diminishes as she takes on more creative projects. Ultimately, Kugayama is a quietly talented individual whose artistic ability, though inconsistent, is genuine, and his journey reflects the everyday struggles of balancing creativity with the demands of real life.