Anji Toni is a supporting character in the story, known as one of the tattooed convicts from Abashiri Prison who possesses a key to a hidden cache of Ainu gold. His background is rooted in the harsh realities of prison labor in Hokkaido. He was among the prisoners forced to work in the sulfur mines on Mount Io, located between Lake Kussharo and Lake Mashu. The toxic fumes from this work permanently destroyed his eyesight, leaving him completely blind. Despite this disability, he survived and eventually returned to Abashiri Prison, where he received his distinctive coded tattoos from the man known as Noppera-Bou.

Anji Toni is portrayed as a highly capable and intuitive individual, forced to rely on his other senses to navigate the world. He has developed a method of echolocation by clicking his tongue, which allows him to effectively visualize his surroundings through sound. He wears a specialized device strapped around his forehead with cup-like structures over his ears to enhance his hearing, further compensating for his lack of sight. His personality is marked by a strong sense of survival and a deep-seated grudge. He holds a significant and merciless hatred for the mining company that caused his blindness and for Warden Shirosuke Inudou of Abashiri Prison. However, he operates with a distinct moral code; although he and his band lead a life of theft to survive, they generally avoid killing their victims unless absolutely necessary. He is a man of quick, split-second decisions and considerable pride in his abilities.

As the leader of a band of blind miners-turned-thieves, Toni terrorized the eastern Hokkaido region, using the darkness to their advantage. His role in the main story begins when his group ambushes the protagonist, Saichi Sugimoto, and his companions while they are relaxing in a hot spring. The attack is notable for taking place in total darkness, giving Toni and his men a tremendous advantage. This confrontation is brought to an end by the intervention of the famous former Shinsengumi commander, Toshizou Hijikata, who recruits Toni and his skills to assist in a planned infiltration of Abashiri Prison.

During the prison break arc, Toni plays a key role, using his unique abilities to navigate the dark corridors. In a significant moment, he separates the Ainu girl Asirpa from her companions to reunite her with her father. Later, his path crosses again with the Seventh Division of the Imperial Japanese Army. He encounters Private First Class Ariko at a remote hot spring and, after fleeing, later disguises himself as a blind masseur (an anma) to infiltrate the Seventh Division's positions in Noboribetsu. There, he eavesdrops on a conversation between Warrant Officer Kikuta and other soldiers, leading to a violent confrontation in the otherworldly landscape of Hell Valley and an old mine filled with ice stalagmites.

Throughout his appearances, Anji Toni forges key relationships based on mutual interest and survival. He works directly under Hijikata, lending his talents to the older man's schemes. He leads a small group of fellow blind survivors, all former miners, who trust him implicitly. His primary antagonists are the soldiers of the Seventh Division, particularly Warrant Officer Kikuta and Private Ariko, who hunt him for his tattooed skin. Despite his primary allegiance to Hijikata, he shows a pragmatic willingness to cooperate with Sugimoto's group when their goals align, even as they remain wary of one another.

Toni undergoes notable development through his trials, particularly during his fight with the Seventh Division. Initially confident in his ability to dominate in darkness, he is forced to adapt when his enemies use tactics like torches to negate his advantage. He demonstrates resilience and cunning, managing to flee from a deadly trap set by Ariko, which involves an avalanche. His journey also involves a complex deception; after being presumed dead in the avalanche, a skin believed to be his is presented to Lieutenant Tsurumi. It is later revealed that this was a fake, and Toni returns to help Ariko escape, having survived the ordeal.

His most notable ability is his use of echolocation through tongue clicking, which allows him to effectively "see" his environment and track the movements of others. This skill, combined with his enhanced hearing device, makes him a formidable opponent in dark or obscured environments where sighted people are at a disadvantage. He is also a skilled marksman, proficient with a firearm he carries in an ammo belt, and can make accurate shots despite his blindness. His physical strength and intuition allow him to hold his own in close-quarters combat, as demonstrated in his fights against both Sugimoto and members of the Seventh Division.