In the early 1900s, following the brutal Russo-Japanese War, a former soldier named Saichi Sugimoto desperately pans for gold in the frozen wilderness of Hokkaido. Nicknamed Sugimoto the Immortal for his supernatural ability to survive deadly battlefields, he seeks a fortune not for greed, but to fulfill a dying promise to a fallen comrade: to support the family he left behind, specifically his widow who needs expensive medical treatment. His luck changes when he hears a tale from a drunken old man about a massive stash of Ainu gold, stolen years ago. The thief, before being captured and imprisoned, murdered the Ainu people who owned the gold and then hid the treasure somewhere in Hokkaido. The only key to its location is a cryptic map, which he tattooed onto the bodies of twenty-four fellow inmates in exchange for a promise of a share of the gold. The old man is soon found dead, killed by a bear, and his body bears the very tattoos described in the story.

Sugimoto is saved from the same bear by a young Ainu girl named Asirpa, whose father was among those murdered by the gold thief. With Sugimotos survival instincts and military prowess, and Asirpas expert hunting skills and deep knowledge of the land, they form an unlikely partnership. They agree to track down the twenty-four escaped convicts, decode the tattooed maps, and find the hidden gold: Asirpa to reclaim what was stolen from her people and understand her fathers fate, and Sugimoto to secure his friends future. However, they are not alone in this treacherous race. The fanatical Lieutenant Tsurumi of the 7th Division of the Imperial Japanese Army seeks the gold to fund a military coup, willing to kill anyone in his way. They are also pursued by a group of rogue former samurai led by the legendary Toshizo Hijikata, who has his own ambitions for the treasure.

The narrative follows Sugimoto and Asirpa across the harsh, beautiful landscapes of Hokkaido as they hunt for the convicts, each one a dangerous and eccentric criminal with unique skills. They are soon joined by Yoshitake Shiraishi, a cunning escape artist and one of the tattooed prisoners, who reluctantly becomes an ally. The story unfolds through a series of notable narrative arcs, each centered on capturing a specific convict or confronting a rival faction. Early arcs like the Introduction and Escape King arcs establish the central conflict and the key players. The Legendary Hunter arc delves into the Ainu culture and the hunt for the last Ezo wolf, while the Battle in Barato arc sees Sugimotos group caught in a yakuza gang war. A significant portion of the story focuses on the scheming of Lieutenant Tsurumi, whose 7th Division serves as the primary antagonist. The plot builds towards a major confrontation at Abashiri Prison, the infamous high-security facility where the original gold thief, known only as Noppera-Bou, is held. The journey forces the characters to navigate shifting alliances, intense survival situations, and the lingering trauma of war, all while showcasing detailed depictions of Ainu traditions, hunting practices, and cuisine. As the hunt continues into Karafuto and confronts the complexities of the convicts pasts, the story expands to include revolutionary movements and deeper conspiracies, pushing the diverse cast of soldiers, criminals, and natives toward a climactic resolution for the legendary Ainu gold.