Kuroiwa is a significant rival in the delinquent drama of Rokudenashi Blues, standing out among the fierce fighters of Tokyo's high schools. He possesses a lean build and a fighting style that emphasizes speed and rapid, unpredictable movements, making him a challenging opponent in the street brawls that define much of the series. Unlike some who fight for pride or thrill, his motivation is deeply personal and shaped by childhood trauma. His father was an ex-convict and former yakuza member who was beaten to death right in front of him, an event that left a lasting scar. This drives Kuroiwa to become the strongest fighter in his school, not for glory but as a means to eventually track down and defeat the person responsible for his father's death, using combat as a path toward vengeance.

His personality is marked by a strong sense of loyalty and a deep need for security. He operates with a tendency to rely on authority figures and established structures, which is reflected in his role as the captain of the baseball team, where he takes his responsibilities seriously and consistently works to improve the team's performance. He values order, routine, and hard work, often emphasizing the importance of practice and discipline. These traits are accompanied by a cautious nature that can veer into paranoia when he perceives a threat to his friends or his circle, causing him to respond aggressively to protect those he cares about. At heart, he is driven by a fear of being left without support, and this fuels his fierce protectiveness and his desire to maintain harmony within his social group.

Within the story, Kuroiwa's primary narrative function is as a rival to the protagonist, Taison Maeda. The competition between them is not simply about who is stronger but is layered with contrasting philosophies: Maeda often fights for his dream of becoming a boxing champion and for the simple love of a good fight, while Kuroiwa fights with a heavy, purpose-driven intensity. This clash creates a tense, dynamic friction that pushes both characters forward. Through their conflicts, Kuroiwa's rigid, duty-bound personality is tested, and his encounters with Maeda challenge his worldview, showing the potential for mutual respect among rivals even when their goals differ. His key relationships revolve around his gang and teammates, to whom he is unquestionably loyal, and the shadow of his father, whose memory dictates much of his life's direction. While his development is largely framed by his pursuit of revenge, his interactions with Maeda and others slowly reveal that strength can be found in bonds rather than in solitary vengeance. His most notable ability remains his unorthodox fighting style, which combines raw agility with a calculating, defensive mindset, allowing him to hold his own against powerhouse brawlers and remain a memorable figure in the violent world of high school delinquents.