Juzou Oki leads the Oki Ocean Lab and designed the advanced SS-99 submarine. Initially, he partnered with the Ocean Empire's military commander Hell Deathbird, developing weaponry like the Z-type aircraft-carrying submarine, but later defected to support humanity's defense.

Grandfather to Susumu and Gorou Oki, he entrusted Susumu with a "99"-marked key to access a hidden lab containing the SS-99 before their survey mission in the Japanese Trench. During this expedition, Ocean Empire forces attacked their submarine, the Kuroshio, capturing Juzou and Gorou.

Imprisoned by the empire, Juzou secretly undermined Hell Deathbird's operations while feeding intelligence on imperial weaknesses to the SS-99 crew. His strategic insights guided the assault that destroyed the Ocean Empire's headquarters.

After the empire's fall, Juzou survived and refined the SS-99 for decades, upgrading it for flight and space travel. These enhancements ultimately enabled interstellar voyages by the 30th century.

Renowned for technical mastery, tactical acumen, and dedication to Earth's safety, Juzou mentors the SS-99 crew. He enforces strict security protocols, exemplified by ordering Susumu to memorize and destroy the submarine manual to thwart enemy capture. His leadership and foresight prove pivotal to the crew's victories against threats.