Following his father's death during the first Dai Apolon battle's destruction, Hideki became the newest resident of Blue Sky Orphanage. His father, the Akabe Dam project's chief planner, had planned a trip to Tokyo with Hideki to report on the dam's near-completion status, but perished in the conflict.

Sent to the orphanage afterward, Hideki vanished on the day scheduled for his departure to the Akabe Dam site. Takeshi discovered him weeping in the forest and persuaded him to proceed with the journey.

En route to the dam, Hideki observed Takeshi transform to confront an attacking monster. He aided the battle by directing UFOs to reflect sunlight onto Dai Apolon, granting the necessary power to overcome the threat. This action led Takeshi to invite Hideki as the fifth and final group member.

Hideki stands as the most intelligent within Takeshi's group and openly displays his intellect, a trait that sometimes borders on arrogance despite his fundamentally good intentions. He operates with strict logic, typically preventing emotions from clouding his judgment.