Hayato Yabuki is introduced as the leader of his class at Kurogin Gakuen, a position that reflects his natural authority among his peers. He shares a deep, complicated history with his childhood friend, Odagiri Ryu, and their fractured relationship forms a central part of his early story. A past fight between them caused Odagiri to quit school and become involved with a dangerous individual, and although Odagiri eventually returns, Hayato continues to hold a grudge over whatever transpired between them.

Initially, Hayato views the persistent class teacher, Yankumi, as an annoying interference in his personal conflict with Odagiri, going so far as to challenge her directly. However, his role in the story evolves as circumstances pull him beyond his personal grievances. On one occasion, he and Odagiri are framed for a series of neighborhood assaults by impostors claiming to be from their school, leading to a situation where no one believes their innocence. In another instance, he chooses to help Kuma, a former student from the previous year, whose shop is being threatened by criminals. This decision is significant because Hayato acknowledges that, having graduated, he can no longer rely on Yankumi to solve his problems, demonstrating a growing sense of personal responsibility.

Key relationships shape his development significantly. His bond with Odagiri is the most pivotal, moving from bitter resentment to a cooperative, if complicated, friendship as they navigate shared dangers. His relationship with Yankumi transforms from antagonism to respect as he witnesses her unwavering dedication to her students. A notable aspect of his background, which explains his initially abrasive personality, is his family. The story introduces Hayato's family to reveal the origins of his "jerky attitude," suggesting that his home life has had a profound impact on his behavior and worldview. His abilities are not supernatural but are grounded in the toughness and street smarts expected of a delinquent leader; he is capable in a fight and possesses the loyalty of his classmates, which allows him to mobilize them when confronting external threats.