Yuuya Nonomura was Tohru Souma's closest friend and mentor within the hacking group Steppenwolf. He played a significant role, teaching Tohru hacking techniques and guiding him in the group. Before Steppenwolf disbanded, Yuuya planned to leave their criminal activities behind, aiming to use his hacking skills legitimately for society and live an honest life.

During Steppenwolf's final operation—a hack into the military organization FLAK's servers—the group became entangled in a conflict between FLAK and the terrorist faction Fei Dao. An unidentified Simulacrum killed Yuuya in this incident. His death spurs Tohru's quest for vengeance and drives Tohru's decision to infiltrate FLAK to uncover the truth behind the killing.

Yuuya possessed light brown skin, contributing to an ambiguously brown appearance despite his Japanese name. He appears only briefly before his death, becoming a posthumous figure who lives on through other characters' memories and motivations. His legacy sets the main storyline in motion and symbolizes the consequences of the hacking group's actions.