Kosuke Entouji is an intelligence division operator for the organization GGG, initially the Gutsy Geoid Guard and later the Gutsy Galaxy Guard. With a recorded IQ of 300, he applies his intellect to a range of critical duties. His primary responsibility is maintaining the extensive computer network at the GGG Baytower Base, a system originally programmed by his father. A key technical achievement was his design of the Z Sensor, a device created to detect Element Z0 particles emitted by Zonder Metal. A prototype wearable version was deployed without authorization by agent Geki Hyuuma to identify the threat designated EI-10. Entouji later refined the sensor for standard GGG deployment, though it remained unable to detect Zonders in human form or the advanced Primeval Zonderians.

He shares a profound bond with the robotic agent Volfogg, who reports directly to him within intelligence rather than to chief of operations Mikoto Utsugi. This connection was powerfully demonstrated when Entouji reacted emotionally to Volfogg's apparent death during the Contra Fall and prepared to send a GGG Area on a kamikaze mission to assist him. Their relationship is rooted in Volfogg's Super AI, which contains the personality of Entouji's deceased partner, Kirio Inugami. A fellow intelligence agent, Inugami was instrumental in laying GGG's groundwork but was killed in action on November 2, 2004, before he could transfer to the formal Intelligence Department.

After the main series, Entouji meets and begins a relationship with a bioengineer called Papillon Noir, who was assigned to the Main Order Room. In the GaoGaiGar FINAL continuity, this Papillon Noir is a replicant from a duplicated Earth. She experiences deep existential angst upon encountering the real GGG team but is reassured by them. This replicant eventually fades from existence following the destruction of her home world, Pisa Sol.