Danji Hiiragi is a 16-year-old war orphan, shaped by Earth's devastating conquest under the Zaar Empire. His past holds a specific darkness: his father was wrongfully executed for a crime he didn't commit, compounding the loss of his mother and leaving Danji utterly alone, fostering deep cynicism and distrust. He survived the post-invasion wasteland solitary until Sanae Shiratori discovered him injured and brought him to the group's hideout at the Adalus base, marking his reluctant integration.

Characterized by blue-themed attire and prominent sideburns (often obscured by his hairstyle), Danji presents a calm, stoic, and reserved exterior. He approaches situations with strategic thinking, forming a sharp contrast to fellow orphan Kento Tate's impulsive and hot-blooded nature. This difference creates friction as they are forced to collaborate. Yet, they share stubbornness and a willingness to use violence, evolving into vitriolic best buds. This partnership is crucial for operating the combining mecha Daltanious: Danji pilots the Gunper spaceship component while Kento controls the Atlaus robot, synchronizing to fuse with the lion robot Beralios.

Danji serves as the grounded counterbalance to Kento's recklessness throughout the conflict. While less overtly expressive, he gradually develops loyalty to the team, particularly towards Sanae, crediting her with saving his life. His development focuses on channeling his traumatic experiences into focused determination during battle, his interpersonal growth remaining subtle. Following the war, Danji remains with the group on Earth to aid in rebuilding.