Gen, whose full name is Gen Inukai, is introduced as a mysterious transfer student who arrives at the same school as the main protagonist, Guren. Initially serving as an antagonist, his trajectory throughout the story is defined by a complex shift from a solitary operative working for the forces of evil to an official and valued member of the Tenkai Knights.

Gen's background is marked by significant personal tragedy. He lost both his mother and father under unclear circumstances, an event that deeply fractured his family and his outlook on life. This loss led him to shut himself off from the world, believing that forming bonds with others was a sign of weakness. In his youth, he was a positive and outgoing child, much like Guren, but the pain of his family falling apart transformed him into a calm, collected, and often stoic individual. He became intensely self-reliant, focusing solely on studying and training to prove his strength and avoid the vulnerability he associated with friendship.

Motivated by his desire for power to overcome his feelings of hopelessness and perhaps even destroy a world that had caused him so much pain, Gen came into possession of the core brick of Dromus. This brick was given to him by Eurus, a guardian of the planet Quarton. Possessing this power allowed him to transform into Dromus, a Tenkai Knight whose appearance is strikingly similar to the hero Bravenwolf but features grey and black armor, distinguished by a scar-like marking on the left eye of his chest plate. Like Guren, he also adopts the descriptor of Tenkai Power to define his fighting spirit.

His role in the story begins as a rival and an antagonist. Working under the primary villain, Vilius, Gen uses his position as a new student on Earth to covertly observe and test the Tenkai Knights, particularly Guren. He is driven to understand their power and prove his own superiority. However, a critical turning point occurs when Vilius steals the Black Dragon Key from him. This act of betrayal forces Gen to re-evaluate his allegiance and his understanding of power. Subsequently, he officially becomes the fifth member of the Tenkai Knights, aligning himself with the Corekai soldiers and fighting alongside his former enemies.

Key relationships heavily influence Gen's development. His most significant connection is with Guren Nash. Gen sees a reflection of his former self in Guren's positive and stubbornly optimistic attitude. Their rivalry is intense, but Guren's unwavering belief in his friends and his refusal to give up eventually pierces through Gen's emotional walls. This rivalry transforms into a deep respect and a strong friendship, with Gen growing particularly close to Guren. He also forms a working relationship with Beni, a female knight with whom he cooperates during his time as an antagonist, and he eventually learns to trust and rely on the other knights, Ceylan, Toxsa, and Chooki, as teammates.

Gen undergoes a profound character development from a lonely and bitter enemy to a heroic ally. His journey is one of healing, learning that strength does not come from isolation but from trust and camaraderie. After formally joining the team, he loosens his guarded personality and becomes a supporter, proving his loyalty and strategic mind. He eventually unlocks an advanced Elemental Mode, known as Dromus Tenkai Whirlwind, which solidifies his place as a true and powerful hero of the story.

In terms of notable abilities, Gen is not only a powerful Tenkai Knight but also a highly skilled martial artist, holding a first-degree black belt. He is an excellent strategist with a deep understanding of Quarton. As the knight Dromus, he wields powers that closely mirror and rival those of Bravenwolf, and his combat skills are consistently shown to be on par with, or even superior to, his teammates in individual disciplines. His ability to unlock an elemental transformation further showcases his immense potential and growth as a warrior.