Hazuki Okamoto, universally nicknamed Okappa, is a high school student and dedicated member of her school's Model Club. She serves as an underclassman to the club's president, Iroe Genma, and shares classes with fellow member Makina Sakamaki, frequently occupying the seat beside her. Okappa maintains a levelheaded and calm exterior but harbors explosive violent tendencies triggered solely by Genma's antics. When provoked, she undergoes monstrously aggressive and sadistic transformations, unleashing physical assaults on people and demolishing objects like desks and walls. This ferocity starkly contrasts her sporadic gentle and nurturing episodes, informally dubbed "Okappa Days." She possesses a pronounced fear of insects, particularly large cockroaches.

Physically, Okappa sports a signature bob-cut hairstyle, occasionally twisted into pigtails. In her early Model Club days, she prominently displayed a model train atop her head, though her enthusiasm for model building eventually faded. Her standard outfit is the school uniform, and she is occasionally illustrated brandishing a baseball bat during her violent outbursts.

Across all official manga and net animation portrayals, Okappa's foundational traits—her composed facade, volcanic reactions to Genma's teasing, and fleeting kindness—persist unchanged. She remains a static force as the club's volatile counterbalance, with no substantive evolution or backstory expansion in extended arcs or spin-offs. Her interactions consistently pivot between icy restraint and frenetic violence, devoid of deeper character exploration.