Yuya Kanzaki arrives as a transfer student at Aiko Tachibana's school, projecting a mature and aloof demeanor belying his youthful appearance. He confronts Aiko with critical information: her current body is artificial, while her original biological body and family remain trapped within Primary Point, the quarantined epicenter of the catastrophic "Burst" incident. He proposes a mission to infiltrate the dangerous zone, offering to accompany her with a team of professional Divers to permanently stop the Burst. His true identity is later unveiled as Toshihide Yura, a prominent Kiryu Biotech researcher presumed dead during the initial Burst. Instead, his salvaged brain was implanted into an artificial organism designated "Unit One" or "Duplicate One" by colleague Susumu Kurose. This existence as an artificial entity fuels his personal objective: atonement for inadvertently causing the Burst. Throughout the mission, he demonstrates strategic acumen and maintains a stoic, reserved exterior, rarely revealing emotion. His relationship with Aiko evolves from necessity to mutual reliance as both grapple with ambiguous humanity—Aiko due to her artificial form, Yuya due to his human brain within a synthetic body. He gradually confronts the ethical weight of his past actions, particularly his involvement in the Artificial Intelligent Cellular Organism (A.I.C.O.) project that triggered the Burst. In the climax, he confronts Dr. Isazu, whose unethical experiments to save his comatose daughter exacerbate the Burst crisis. Yuya's technological knowledge and connection to the Malignant Matter prove pivotal in resolving the conflict. Following the mission's success and Aiko's restoration to her original body, he survives. His physical appearance is noted as black-haired, blue-eyed, and approximately 5'8" tall. The epilogue detailing other characters' fates does not show him.