Manjiro is an impoverished 14-year-old Japanese fisherman with a deep desire to become a samurai. When shipwrecked and rescued by American whalers, his inquisitive nature helps him adapt to a completely foreign culture. Unlike his cautious friends, he actively seeks to learn English and understand the broader world. He continually works to bridge the gap between his Japanese heritage and the new American customs he encounters.

Captain Whitfield is the commanding officer of the whaling ship John Howland. With his striking one-eyed gaze and imposing appearance, he initially intimidates the stranded boys. He quickly proves to be a fair-minded leader who encourages Manjiro's questions and offers him protection. He eventually invites the boy to America to be his adopted son, providing him with a stable family life.

Jolly is an American whaler with golden curls and a deeply hostile attitude toward the rescued Japanese fishermen. Harboring intense racial prejudices, he goes out of his way to intimidate and threaten Manjiro. He refuses to view the foreigners as equals and holds long-standing grudges against anyone who reprimands him.

Tom is a tall student in Massachusetts who aggressively bullies Manjiro. Coming from a wealthy family that owns fast horses, he actively tries to alienate anyone who befriends the new foreign student. His outward cruelty masks a troubled home life involving an abusive father.

Denzo is one of the older Japanese fishermen stranded at sea with Manjiro. Serving as a cautious leader among the group, he maintains traditional values and strongly distrusts the American sailors. He constantly worries that foreign customs are corrupting the younger boys.

Goemon is a young fisherman and one of Manjiro's closest companions during their shipwreck. Terrified of the ocean and deeply conservative in his outlook, he begs Manjiro to stick to what is familiar. He acts as a foil to Manjiro's adventurous spirit by warning him against trusting the American whalers.

Jusuke is one of the original five fishermen caught in the storm that strands them in the Pacific Ocean. He relies heavily on routine and remains wary of the foreigners who rescue them, preferring to isolate himself from the crew.

Toraemon is another of the Japanese fishermen shipwrecked on Bird Island. He shares the group's general suspicion of the American crew and longs to return to the safety of Japan's borders.

Originally from New York, Mrs. Whitfield marries the captain and helps establish a farm in Massachusetts. She forms a stable household for Manjiro, becoming his American mother figure. She is fiercely egalitarian and actively defends Manjiro against racism in their community.

Terry is an energetic local boy who becomes Manjiro's primary companion in Fairhaven. He is highly receptive to learning about samurai culture and treats Manjiro as an absolute equal. He serves as an enthusiastic guide in America and constantly dreams of finding wealth.

Catherine is a sweet local girl who captures Manjiro's teenage affections. Though she likes Manjiro and expresses openness to his romantic gestures, she is constrained by the racist attitudes of her peers.

Job is a student at the Bartlett School of Navigation who quickly befriends Manjiro after an initial prank. He accepts Manjiro's differences and supports him against the school's resident bullies.

William Henry is the biological infant son of Captain and Mrs. Whitfield. As a baby, he is a source of immense joy for Manjiro, who dreams of bringing his little American brother to visit Japan one day.

Ira Davis begins as a first mate and later captains the whaling ship Franklin. He lures crew members into low-paying positions with vague promises. His leadership style relies on intimidation and physical threats, making voyages under his command deeply tense.

Mr. Aken is a sailor and the son of close friends to the Whitfields. He serves as a familiar, stable presence during difficult whaling voyages and maintains his professionalism even when commanding officers behave erratically.

Lord Nariakira is a high-ranking Japanese daimyo with strict authority over commoners. Despite enforcing Japan's isolationist laws, he possesses a cold curiosity about the changing world. He specifically seeks out information regarding Western technology and military strength.

Dr. Judd is a collector of Japanese artifacts living in Honolulu. He shows the rescued fishermen a world map, which profoundly shifts their understanding of Japan's geographic size relative to the rest of the globe.

Plum Duff, affectionately renamed Duffy, is a pony-sized horse on the Whitfield farm in Massachusetts. She provides quiet comfort to Manjiro and participates in local races, proving to be a small but spirited animal companion.

Tori is a parrot named after the Japanese word for "bird." As an animal displaced from its natural home, the bird travels on whaling ships and serves as a quiet companion to sailors far from their families.

Mr. Hussey is a local cooper who takes on young men as apprentices to teach them a trade. He runs a strict operation, often failing to provide adequate food or comfortable conditions for the workers under his care.