Toshiyuki Roberi teaches math at Imazuru Prefectural High School. Recruited to oversee the newly formed Prefectural Earth Defense Force against the Telephone Pole Gang, he pragmatically uses its security budget to pay students for their participation. His small second-floor apartment becomes crucial to the Force's operations after he discovers the injured cyborg exchange student Karmi Santin collapsed in the street and takes him in to recover, leading to Santin joining the group. Following the destruction of the original Defense Force building in a clash with the Gang and its rebuilding, Roberi's residence serves as the informal headquarters.

Roberi encounters Telephone Pole Gang operative Ryūko Harataki, infiltrating the school under the alias Colonel Baradagi. As part of her mission to discredit him, Harataki attempts seduction. Roberi misinterprets her advances as a plea for academic help from a struggling student desperate for better grades. Responding professionally, he invites her to discuss her situation over a meal.

Throughout the conflict, Roberi acts as faculty advisor to the Defense Force. He provides logistical support, gathering intelligence on the Gang's headquarters and facilitating the use of his apartment as the operational base, focusing on coordinating student members rather than frontline combat.