Hyakunosuke Ogata is a central character in the narrative, known for his exceptional skill as a sniper and his deeply inscrutable nature. He was born as the illegitimate son of Kojiro Hanazawa, a former lieutenant general of the Seventh Division, and a geisha named Tome Ogata. Raised primarily by his maternal grandmother in Ibaraki Prefecture, his childhood was marked by the absence of parental affection and the social stigma of his birth, which deeply informed his worldview. Ogata served as a Superior Private in the Seventh Division of the Imperial Japanese Army, a veteran of the Russo-Japanese War, but his true loyalty has always been to himself, pursuing the hidden Ainu gold for reasons he never fully articulates to others.

Ogata possesses a cold, analytical, and ruthless personality, earning him nicknames such as "the Wildcat" and "the Lone Lynx". He is a proud and calculating individual who prefers to observe situations from a distance, evaluating the most efficient course of action with a detached pragmatism. On the surface, he can act amiable and polite, but he is adept at lying and deception to achieve his goals, often delivering caustic remarks about the incompetence he perceives in others. He does not hesitate to kill and claims to feel no remorse, developing a twisted philosophy that all people are inherently remorseless killers like himself. This belief leads him to experience cognitive dissonance when encountering individuals who contradict this view, such as his half-brother or Asirpa, as he cannot understand or accept innate kindness or moral restraint.

His primary motivation is rooted in his fractured family history. He harbors a deep-seated resentment towards his father, who rejected him and his mother in favor of a legitimate family. Ogata views patricide as a rite of passage into adulthood and ultimately killed both his father and his younger half-brother, Yuusaku Hanazawa. Yuusaku was a virtuous and well-liked officer whose inherent goodness and reluctance to kill stood in stark contrast to Ogata's own nature, generating a complex mix of jealousy and guilt that haunts him. His pursuit of the gold is less about material wealth and more about a personal, elusive goal tied to these deep psychological fractures, making him a wildcard whose actions are difficult to predict.

Throughout the story, Ogata shifts between multiple factions without ever truly belonging to any. He begins as a member of Lieutenant Tsurumi's faction within the Seventh Division but betrays them, leading a small rebel group of his own before temporarily aligning with Hijikata Toshizou's group. He later forces an uneasy alliance with the protagonist, Sugimoto Saichi, and the Ainu girl Asirpa, only to repeatedly attempt to kill them. His role is often that of a catalyst, creating chaos and forcing confrontations through his unpredictable violence. His key relationships are defined by conflict. He shares a murderous rivalry with Sugimoto, which results in a near-fatal fall that leaves Ogata with distinctive scars on his cheeks after a severe jaw fracture. His relationship with Asirpa is particularly fraught; he reveals himself as the sniper who killed her father, Wilk, in an attempt to prove his nihilistic philosophy by goading her into becoming a killer like him.

Ogata undergoes significant physical and psychological development. Following his fall from a cliff, he receives facial surgery that leaves permanent scars. Later, he loses his right eye after being struck by one of Asirpa's poisoned arrows, eventually covering the wound with a bandage before acquiring a prosthetic eye. Psychologically, his carefully maintained emotional detachment begins to crack. He suffers from haunting visions of his dead half-brother, suggesting that he is not as free from guilt as he claims to be. His attempts to force others, particularly Asirpa, to confront their own capacity for murder stem from a desperate need to validate his own broken identity.

His most notable ability is his extraordinary marksmanship. As a sniper, he is capable of accurately hitting a target's head from over 300 meters away using only a standard issue Type 30 rifle and his natural vision. He possesses immense mental fortitude, allowing him to remain perfectly still for extended periods in harsh weather conditions to fool opponents. His hearing is also very acute, able to identify the type of rifle from its gunshot, and he is fluent in Russian, a skill he keeps largely hidden. Despite these strengths, he is notably weak in melee combat, preferring to rely on his ranged superiority or escape from close-quarters fights he cannot win.