Moriki Miyuki is the analyzer and a crew member aboard the experimental submarine SS-99, designed by Dr. Juzou Oki to counter the Ocean Empire's threat to Earth's oceans. As the only female member of the Ocean Agency crew, she is responsible for maintaining, repairing, and operating the SS-99, with her technical expertise being central to the vessel's missions.

Miyuki displays maturity beyond her years, exhibiting intelligence and resourcefulness in solving mission-critical problems. She commands the respect of her male colleagues as an equal despite her youth. Her commitment to the Ocean Agency involves a strong dedication to protecting marine environments and their inhabitants, often prioritizing this goal above personal safety.

Her character involves confronting new challenges and gaining deeper insights into her role across missions. She proactively anticipates operational issues, employing logical, methodical problem-solving techniques. Miyuki also demonstrates empathy and compassion, frequently prioritizing the needs and emotions of others.

Personality assessments describe her with traits of loyalty, duty, and responsibility, aligning with an ISFJ personality type. Her motivations include a desire for recognition and emotional connection, consistent with Enneagram Type 2 characteristics.

Miyuki has blonde hair and is a teenager, though her exact age is unspecified. Her background details, family history, and development beyond the main series episodes are limited to documented sources.