Hiroshi Kuronaga is a student from the third-year class at Shiroiwa Junior High School in the fictional city of Shiroiwa, Kagawa Prefecture. He is a fifteen-year-old citizen of the Republic of Greater East Asia. Hiroshi is described as one of the shortest boys in his class, though his physical build differs between adaptations; in the novel he is notably short, while in the manga he is depicted as robust and intimidating, comparable to the larger student Yoshio Akamatsu.

In terms of personality, Hiroshi is characterized as a quiet and arrogant individual. He is less openly aggressive than his friend Ryuhei Sasagawa, but is still considered by classmate Toshinori Oda to be one of the more violent members of the class. This violence is shown in the manga, where he bullies Yoshio Akamatsu, forcing him to buy lunch and berating him for incorrect orders. His motivations throughout the Program appear to be primarily focused on survival through group allegiance, though he ultimately follows instructions from others without seeming to question them.

Hiroshi is an occasional member of the gang led by the class's most formidable student, Kazuo Kiriyama. His association with this group is not born from genuine friendship but from awe and fear of Kiriyama. Within the group, his closest associate is fellow member Ryuhei Sasagawa, with whom he is frequently seen. The other core members of this affiliation include Mitsuru Numai, Sho Tsukioka, and Izumi Kanai.

During the Program, his role is to serve as one of the minor antagonist figures, part of the group of students who are more inclined toward violence and bullying. His designated weapon varies by adaptation; in the novel and manga he receives a harisen, a paper-fan often used for comedic or disciplinary striking. In the film adaptation, his assigned weapon is a dagger. His interactions are largely confined to his fellow gang members, and he has no meaningful connection to the central protagonists, Shuya Nanahara or Noriko Nakagawa.

His death occurs in all versions at the hands of Kazuo Kiriyama, demonstrating the ruthless nature of Kiriyama and his willingness to eliminate even those who consider themselves part of his group. In both the novel and the manga, Kiriyama sends a message to Hiroshi and the other gang members instructing them to gather at the southern tip of the island once the students are released from the school building. Hiroshi follows this instruction without hesitation. Upon his arrival at the designated meeting point, Kiriyama immediately stabs him, killing him before he can even use his weapon. In the manga, he is likely killed before Ryuhei Sasagawa, as his body is shown lying on the ground.

In the film adaptation, Hiroshi is instead part of a group led by Mitsuru Numai. This group, consisting of Hiroshi, Ryuhei Sasagawa, Sho Tsukioka, and Izumi Kanai, confronts Kazuo Kiriyama and accuses him of being a spy for the Program's supervisor, Kitano. During this confrontation, Kiriyama creates a distraction by spitting his chewing gum at Ryuhei Sasagawa, allowing him to disarm Sasagawa of his Uzi submachine gun and then shoot the entire group, including Hiroshi.

He possesses no notable abilities or special skills that distinguish him within the narrative. His only significant action is following orders, and he fails to survive long enough to make any meaningful choice or take any independent action that affects the outcome of the Program. His character serves primarily to illustrate the dynamics within Kiriyama's gang and to demonstrate the swift, brutal, and indiscriminate nature of the Program, where even a student who believes himself to be aligned with the strongest player is immediately eliminated without mercy.