Gen Kurai is a supporting character who initially serves as a rival before becoming an ally to the main group of heroes. He is a thirteen-year-old boy with a tall, lean build, red eyes, and spiky auburn hair pushed back from his face, with long bangs covering one of his eyes. His typical attire consists of a high-collared black jacket that often covers his mouth, secured by buttons on each side, matching black pants held up by a belt with a gold buckle, and black boots.

Initially, Gen Kurai's personality is cool, calm, and collected. He holds a dismissive view of those who rely on teammates, believing such dependence indicates weakness. This aloof demeanor, however, is not his original nature. In the past, he was a positive and outgoing child, very similar in temperament to the main protagonist, Guren. The specific event that triggered his personality change is not revealed. As the story progresses, particularly after a turning point, his attitude toward others softens, and he eventually joins forces with them.

Gen's background is tied directly to the world of Quarton, as he is the human host for the core of Dromus, a formerly evil entity who bears a strong resemblance to the hero Bravenwolf. His role in the story is complex; he acts as an antagonist who challenges the Tenkai Knights, yet his actions are driven by a personal, painful history rather than pure malice. He transfers to the same school as the main protagonists, allowing him to observe and test them in their daily lives. Gen competes with them in various activities, such as basketball and chess, often proving himself to be slightly more skilled. His rivalry with Guren is particularly significant, as Gen becomes curious about whether Guren is Bravenwolf and eventually confirms his suspicions. Throughout the middle portion of the narrative, Gen aligns with another character named Beni in efforts to oppose the Knights, and he successfully obtains a powerful artifact known as the Black Dragon Key. However, after an intense confrontation where Guren learns about the depressing circumstances of Gen's life, a shift occurs. Gen ultimately experiences an epiphany and chooses to help the other Knights defeat the main villain, Vilius, restoring balance to Quarton.

The key relationships in Gen's development are with Guren and, to a lesser extent, Beni. Guren persistently tries to reach out to Gen and understand his motivations, which becomes the catalyst for Gen's eventual change of heart. Beni, an ally during his rogue phase, lectures him about the difficulties of working with him, an interaction that directly precedes his decision to join the Knights. After his redemption, Gen takes on the role of breaking the Tenkai Dragon back into its component cubes and saves the other Knights during a later crisis.

Gen possesses several notable abilities. He is a skilled strategist who demonstrates a deep understanding of Quarton and its workings, often more so than he initially reveals. His talents are not limited to combat and strategy; he is also portrayed as exceptionally proficient in physical and intellectual contests, including basketball and chess, where he habitually performs one level above the other main characters.