Goro Oki holds the position of deputy officer at the Oki Ocean Lab, operating under his grandfather, Dr. Juzou Oki, the facility's leader. He is the older brother of Susumu Oki, with both siblings actively engaged in the lab's operations and the conflict against the Ocean Empire.

At the story's beginning, Goro provides his younger brother Susumu with a modified World War II-era Type 99 rifle. He also gives Susumu a key marked "SS-99," originally entrusted to them by their grandfather Juzou. This key possesses significance for accessing or operating the advanced submarine developed by their family.

Goro accompanies Juzou on a critical survey mission aboard the exploration submarine Kuroshio to investigate mysterious attacks in the Japanese Trench. During this expedition, their submarine is attacked by an unidentified hostile vessel associated with the Ocean Empire. Following this assault, the surface ship Kairyumaru loses contact with the Kuroshio.

While Goro's role in initiating the conflict investigation and his familial relationships are confirmed, his fate after the attack on the Kuroshio remains undocumented. His character does not reappear in any subsequent documented episodes or events. No further development, interactions, or resolutions involving Goro Oki are detailed across any official media, including potential spin-offs or expanded universe content.