Eddie Dun is an American expatriate who runs a horse ranch in the Hitaka region of Hokkaido. As a middle-aged man of American descent, he has a distinctive appearance characterized by his shoulder-length graying hair, bushy eyebrows, and a thick mustache. His manner of dress reflects his Western origins, as he typically prefers suits, shirts, frock coats, and accessories such as cravats.

Eddie Dun possesses a passionate interest in collecting a wide array of items, including weapons, rare objects, and artifacts, with a particular appreciation for Ainu cultural pieces. He is portrayed as a greedy individual who is largely preoccupied with his wealth and personal possessions. Despite this focus on material gain, he maintains a strong sense of care for his ranch and the horses he raises, showing a willingness to negotiate with others who can assist him in dealing with threats to his property.

In the story, Dun becomes involved with the main characters when it is revealed that he has come into possession of an heirloom garment belonging to Asirpa's great-aunt. When confronted by Sugimoto and Asirpa, he refuses to return the garment for the original price of thirty yen and instead demands they pay one hundred yen. Before any conflict can fully develop, a frightened man interrupts to report the return of a monster that has been terrorizing the area. Dun explains that this creature is actually a bear which has previously attacked his horses. He had managed to shoot the bear multiple times, injuring its claws and eyes, but he believes the animal is impossible to kill because all its wounds seem to disappear.

Dun later assists a yakuza boss named Oyabun, who demands the largest weapons in his collection. He accompanies Oyabun in a car while the yakuza boss fires a Maxim gun that he had taken from Dun's arsenal. After the situation involving the bears and the yakuza is resolved, Dun honors his agreement and hands over Asirpa's great-aunt clothing to Sugimoto's group in exchange for the thirty yen.

During this exchange, he observes Asirpa admiring a bow and inquiring about its creator, noting that the craftsmanship is incredible. Dun states that a famous old hunter in Hidaka had given him the bow, and he offers to give it to her since her own bow was broken during the battle with the bears. In return for this gesture, he expresses a desire to know the purpose behind the tattooed skins that Sugimoto's group has been investigating. Sugimoto declines to share this information, citing safety concerns for Dun himself.

Dun then produces a book from a chest, which horrifies Shiraishi as it is revealed to be made from a human face. He explains that a man killed by the bears had given him the book, which had many previous owners, including a thief who had stolen it from its creator in Yubari. He adds that this thief had looked inside the book and seen a skin bearing a very unusual tattoo, providing Sugimoto's group with a vital clue that sends them onward to Yubari.

Eddie Dun serves as a supporting character who provides both material resources and crucial information to advance the main characters' quest. His role demonstrates how the search for the tattooed prisoners intersects with various inhabitants of Hokkaido, each with their own interests and connections to the region's history. His primary abilities appear to be related to his knowledge of weaponry, his collection of rare and unusual artifacts, and his operation of a functioning automobile, which is a notable technological asset in the late Meiji period setting of Hokkaido.