Lagos acted as an older brother figure to Patema in the underground society, mentoring her and igniting her curiosity about the forbidden outside world. He regularly defied the Elder's explicit prohibitions to venture beyond the tunnels, returning with trinkets and stories from the surface. Before a significant journey, he gave Patema a polaroid photograph depicting a wide open field, inscribed with "The Real World," which shaped her perception of the surface and fueled her desire to explore it.

Exploring the surface, Lagos befriended Age's father. Both shared a fascination with the sky and gravitational anomalies. They collaborated on scientific experiments to understand the inverted gravity and jointly constructed a flying machine designed to explore the mysteries above Aiga, demonstrating a mutual commitment to bridging their worlds through ingenuity and trust.

After Age's father fell to his death during the flying machine's public demonstration, Lagos returned underground. He later disappeared during another unauthorized surface expedition, leaving Patema without closure. Lagos had been captured by agents of Aiga's leader, Izamura. He died in captivity, and Izamura preserved his body in a glass stasis chamber as a macabre trophy and warning against defying Aiga's authority.

Lagos's legacy continued to shape events long after his death. Age and Patema discovered his notes and research within the flying machine hidden above the artificial sky. These materials provided crucial insights into the true nature of their worlds, helping expose Izamura's lies about the gravity inversion's origins and the shared history. Lagos's pioneering spirit and defiance of isolationist policies ultimately inspired unification efforts between the underground inhabitants and Aiga's citizens.