Rikimatsu Ariko, also known by his Ainu name Ipopte ("to bring to a boil"), is an Ainu man from near Noboribetsu in Hokkaido. He possesses a muscular build, dark complexion, and long black hair secured in a bun. His face features a prominent scar closed with five stitches, a tuft of beard on his chin, large eyebrows, and noticeable chest hair, contributing to a stern appearance. As a child, he was pudgy with a stout nose, thick lips, and a small patch of hair on his bald head. Ariko serves as a Private First Class in the Imperial Japanese Army’s 7th Division. In his youth, he navigated Penkeyu’s mines during winter, memorizing their multiple exits. He later joined the Mount Hakkoda search and rescue operation for the 5th Infantry Regiment. His father, Siromakur Ariko—one of seven Ainu who gathered gold for Hokkaido’s independence and discovered Kimuspu—died while carving a traditional Ainu Makiri knife for him. This event later fueled Ariko’s regret for not learning Ainu customs from his father. Ariko’s personality blends military loyalty with evolving cultural awareness. Initially indifferent to Ainu-Wajin distinctions, he viewed traditions as burdensome yet retained knowledge of customs like locating secret hot springs and identifying traditional clothing. A transformative moment occurred when he encountered a tattooed convict at a hot spring, mistaking the tattoos for patterns. A village elder corrected him, sparking deeper engagement with his heritage. During the Battle of Mukden in the Russo-Japanese War, Ariko and Warrant Officer Kikuta were trapped in a bombed trench. To stay conscious, Ariko shared his regret over disregarding his father’s Makiri craftsmanship, acknowledging its role in connecting Ainu generations. This confession deepened his bond with Kikuta, who harbored guilt over Siromakur’s death. In the 7th Division, Ariko pursued the tattooed convict through a mine from his childhood, triggering an avalanche to kill him. He recovered the tattooed skin as a gift for Lieutenant Tsurumi. Tsurumi later discovered Ariko’s secret collaboration with Hijikata’s group, coercing him into becoming a double agent under threat to his family. To maintain cover, Usami brutally beat Ariko on Tsurumi’s orders, allowing him to infiltrate Hijikata’s faction. There, he stole six tattooed skins—one genuine and five fakes crafted by Edogai—to sabotage Hijikata’s decoding efforts. Hijikata anticipated the theft, revealing a strategic duel between the factions. Ariko’s arc culminated in sacrificial death while protecting others, aligning with his father’s unrealized goal of Ainu autonomy and marking his transition from apathy to commitment.