Tamon Mikuniya is the owner of the merchant ship Solarismaru, a vessel used for foreign trade. He is a wealthy and practical merchant, characterized by a strong focus on profit and material gain. His primary motivation in the story is to navigate his ship successfully and conduct his commercial ventures. Tamon Mikuniya relies on a compass embedded in the ship's structure to guide his voyages, a tool that reflects his methodical and worldly nature. He appears during the Umibōzu arc, where his ship becomes the setting for the encounter with the sea monster and the Medicine Seller. His role in the story is largely functional: he provides the vessel that carries the passengers into the Dragon's Triangle, and he represents the merchant class of the Edo period. His key relationship is with his assistant Goromaru, who serves him aboard the ship. Tamon Mikuniya does not undergo significant character development; he remains a steady, business-minded figure throughout the arc. He has no supernatural abilities, but he demonstrates practical seamanship and a keen sense of navigation.