Hayato Nangou is a Maritime Self-Defense Force officer who begins as a third-grade officer and rises through the ranks to become a second-grade officer. Initially serving as Executive Officer aboard the submarine 707 under Captain Youhei Hayami, he acts as the captain's principal subordinate. His duties involve supporting command decisions and managing crew operations during critical combat engagements against the USR organization.

Nangou participates in the Peace-Keeping Navy's inaugural meeting, which is disrupted by Admiral Red's attack. During this assault, the original submarine 707 is destroyed after intercepting a torpedo aimed at the flagship. Following this loss, Nangou joins the crew of the newly commissioned submarine 707 II, resuming his position as Executive Officer for missions against the USR fleet.

In one operation, he contributes tactical expertise when the submarine becomes trapped in a freshwater crater, preventing normal surfacing. The crew must coordinate complex maneuvers to evade enemy torpedoes and escape the predicament. These high-stakes scenarios showcase his leadership and operational skills. Nangou's career culminates in a promotion to captain of the submarine 717, marking his significant advancement within the Maritime Self-Defense Force hierarchy.