Gorō Kusaka serves as a crew member aboard the submarine 707 II, successor to a vessel destroyed in prior combat. Initially introduced as a trainee alongside Kenji Minahaya and Senta Umino, he advances to full crew status under Captain Hayami Youhei. His duties contribute to the submarine's operations during confrontations against adversarial forces commanded by Admiral Red. In a critical engagement, the 707 II suffers severe attacks from these forces, forcing evasive maneuvers into a valley for concealment. Admiral Red attempts to destroy the valley, aiming to immobilize the submarine within resulting mud torrents. The crew, including Kusaka, narrowly escapes this trap by maneuvering into a crater containing a pure water layer, a challenging environment for buoyancy control. The vessel subsequently endures a concentrated torpedo assault while positioned within this crater.