Serge Borough, a key operative within the clandestine Secret Society, executes covert missions under Albert Killy’s command to protect the organization’s covert military ventures and geopolitical interests. During the Uoodo arc, he adopts the guise of a spiritual guide to oversee Fyana—Proto-One, a prototype Perfect Soldier engineered for warfare. Tasked with refining her combat capabilities and enforcing obedience to the Society’s agenda, he voices doubts about her emotional volatility and inferior design compared to successors like Ypsilon.

When Chirico Cuvie disrupts the Society’s plans, Borough pivots to eliminate him, engineering clashes between Chirico and enhanced soldiers under his command, including Proto-One. After Uoodo’s annihilation by Melkian forces, he infiltrates Kummen’s political sphere via an alliance with its prince, exploiting regional instability and military assets to hunt Chirico with ruthless precision.

Borough’s supervision of Ypsilon exposes his wariness toward embedding human-like emotions in artificial warriors. He criticizes allowing Ypsilon prolonged interaction with Fyana, fearing it may erode programmed loyalty. Despite these misgivings, he adheres to orders, preparing Ypsilon for combat while grappling with the soldier’s volatile reactions to perceived slights—a flaw underscoring the Society’s imperfect creations.

Collaborating with twin engineers Arron and Gurran Schmittel, Borough enforces tactical and ideological cohesion across the Perfect Soldier program. Yet Chirico’s tenacity and the soldiers’ emergent autonomy—particularly Fyana’s defiance—undercut his efforts. His unyielding chase of Chirico persists, mirroring the Society’s struggle to dominate forces slipping beyond their grasp.