Jukichi Oyama is the master fisherman and owner of the fishing vessel Taihei-maru, its name "calm circle" reflecting his approach to life and work. His physical appearance bears the marks of a lifetime at sea: sunburnt skin like well-tanned leather, hands etched with grimy wrinkles indistinguishable from old fishing scars, all deeply creased by sun exposure. Seldom laughing, he maintains calm good spirits and never raises his voice, even in anger or when commanding his boat.

As a mentor to young fishermen Shinji Kubo and Ryuji, Jukichi imparts wisdom extending beyond fishing techniques. He emphasizes patience and respect for nature's forces, teaching these virtues are essential for navigating life's challenges. His guidance proves pivotal when he advises Shinji and Ryuji against violently confronting Yasuo Kawamoto, who spreads malicious rumors about Shinji and Hatsue Miyata. Jukichi counsels leaving "a fool" alone, stressing that patience remains key, drawing a direct parallel to fishing: "That’s what it takes to catch a fish."

Jukichi actively supports Shinji's romantic pursuit of Hatsue by facilitating secret communication through letters after her father, Terukichi Miyata, forbids contact. He later plays a crucial role in resolving the central conflict by suggesting Terukichi have both Shinji and Yasuo serve apprenticeships aboard one of his freighters. This arrangement allows Terukichi to evaluate their characters firsthand, with Jukichi's recommendation carrying weight due to his respected judgment. Shinji's demonstrated courage during a storm aboard the vessel ultimately validates Jukichi's faith in him.

His profound connection to the sea shapes his worldview. He views it not as a realm for grand adventures but as a "rippling field" where fishermen earn their livelihood. This perspective influences Shinji's understanding of harmonizing with natural forces rather than conquering them, extending the lesson to broader life principles.