Nathan Bilstein serves as an engineer at Rebuild, the manufacturing firm established by Jacques Yvain. He maintains a close friendship and professional partnership with Derrida Yvain, Jacques' son. Nathan and Derrida jointly uncover a critical programming flaw within the Autonomous Machine DZs, robots essential to Rebuild's functions. They alert their superior, Hans Andrei, to this dangerous bug, but he dismisses their warnings, intending to exploit the flaw for military applications.

As a single father, Nathan diligently cares for his young daughter, Mage Bilstein. He hosts a birthday celebration for Mage, attended by Derrida and her friend, Yuri Dietrich. During this gathering, Nathan proposes collaborating with Derrida on time leaping research, an offer Derrida refuses. Nathan also provides Derrida with an access key for a DZ patch meant for Mage.

The day after the birthday party, Nathan and Derrida face an attack by militarized DZs, deployed under Andrei's orders following their attempt to rectify the DZ flaw. Jacques Yvain is murdered by Andrei's agents during their escape. While Nathan and Derrida try to flee the city, Andrei intercepts them, aiming to frame Derrida for Jacques' murder. Nathan is killed in this confrontation, his final words a desperate plea to Derrida: "Take care of Mage."

Nathan's death and his final request become the driving force for Derrida after Derrida awakens from a ten-year cryogenic sleep. Nathan's earlier research into time leaping indirectly relates to Derrida's subsequent experiences with temporal anomalies, including visions of Mage manifesting as "Ange." Nathan's legacy endures through Derrida's ongoing journey to fulfill his promise to protect Mage in the war-torn future.