Okabe employs protagonists Hiroki Fujisawa and Takuya Shirakawa at his military parts factory in Aomori Prefecture during their middle school years. He supervises their part-time work assembling and delivering aircraft components for military contracts, assigning demanding tasks with a stern, commanding demeanor. Despite his gruff exterior and tendency to underpay the boys, he quietly supports their personal project by offering technical guidance, tools, and expertise after hours to help build their aircraft, the Velaciela (also known as Bella Ciela or Bela Ĉielo).

His personality shifts noticeably between contexts: authoritative with employees yet visibly nervous and awkward around women, especially their classmate Sayuri Sawatari. Beyond the factory, Okabe secretly leads the Uilta Liberation Front, an underground group fighting to reunify Japan by ending the Union's occupation of Hokkaido (called Ezo). His motivation stems from personal loss, as his family became trapped in Hokkaido after Japan's postwar division.

Three years after Sayuri's disappearance, as political tensions rise, Okabe recruits Takuya into the Uilta Liberation Front. He reveals their plan to destroy the Hokkaido Tower with explosives, aiming to trigger war between US-allied South Japan and the Union to force reunification. Learning of Sayuri's connection to the tower's dimensional instability, he coordinates with Professor Tomizawa to locate her. During the climax, Okabe supplies Hiroki and Takuya with a missile to destroy the tower, aligning their mission to save Sayuri with his organization's goal of neutralizing this Union strategic asset.

Following the tower's destruction, which halts its matter-replacement effect, Okabe's reaction indicates satisfaction with the outcome.