Hangan Nagamine commands the Toibarai military unit garrisoned at Kanatanoki Castle on Tsushima Island. A descendant of exiled Sakimori soldiers historically charged with defending Kyushu, his lineage roots him deeply within the island's defense forces. Nagamine bears the distinctive purple facial tattoo marking all male Toibarai members on his left cheek.

He first appears concealed behind a wooden mask, later revealing his face to assume direct battlefield command against the Mongol invasion. Strategically coordinating defenses and vital reinforcements with allies like Kuchii Jinzaburō and Princess Teruhi, Nagamine leads his unit in critical actions, including rescues during pivotal confrontations, demonstrating unwavering commitment to Tsushima's protection.

The conflict escalates as promised reinforcements from the Kamakura Shogunate fail to arrive, a political betrayal abandoning Tsushima as lost. Facing overwhelming Mongol numbers, Nagamine's forces fight increasingly desperate defensive actions. During the defense of Kanatanoki Castle, he sustains mortal wounds yet rallies his remaining troops for a final stand. Nagamine meets his end defiantly on the battlefield, inspiring his men to fight until overwhelmed.

His documented story concludes within the main series, with no sequel manga or other media expanding his legacy or backstory.