Ryuji is Hikaru's childhood friend and "soul mate".
Korean name: 루키 (Rookie)
Hikaru and Ryuiji met during elementary school when Ryuiji challenged into dares causing mischief. One day, Ryuji slipped and hung on to a branch for his life. Hikaru managed to save him, causing their friendship. Then his soul mate told him that he'll become a member of Rescue Force and protect others and make them smile.
During a Super-disaster, Ryuiji went to an autitorium that was a refuge during the crisis, Ryuiji recognized Rescue Force's R1 as Hikaru. Ryuiji was glad that his soul mate has obtained his dreams.
Ryuiji decided to follow Hikaru's example and became a camp counselor for some village kids. He met Hikaru again when Ryuiji was hanging on to a branch. After Hikaru "saved" him, he explained how Hikaru has brought impact on him. He was even more impressed that he knows Kirara Amamiya , the beautiful weatherwoman, just what he expected from his soul mate.