Hyakunosuke Ogata is a former Superior Private of the 7th Division of the Imperial Japanese Army, known as a lone sniper with the nickname "Wildcat". His background is marked by a troubled family history as the illegitimate son of Lieutenant General Kojiro Hanazawa, a high-ranking commander, and a geisha named Tome Ogata. After being abandoned by his father, his mother's mental health deteriorated, leading to her institutionalization; Ogata ultimately killed her in what he considered a test to see if his father would react. He later killed his younger half-brother, Yusaku Hanazawa, on the battlefield and, at the instigation of Lieutenant Tokushiro Tsurumi, murdered his father in a manner made to look like suicide.

Ogata possesses a cold, analytical, and ruthless personality, viewing the world through the detached lens of a sniper. He is extraordinarily proud of his marksmanship skills, which he honed from childhood, and he maintains his composure even in dire circumstances, always seeking the most efficient course of action. He does not hesitate to kill and feels no remorse, having adopted a twisted philosophy that all people are inherently remorseless killers at heart, a belief that creates intense cognitive dissonance when he encounters those who contradict it. On the surface, he can act amiable and polite to deceive others, but he is prone to caustic remarks and openly looks down on those he considers incompetent. He considers patricide a rite of passage and struggles to empathize with others, often leading him to misinterpret their actions.

In the narrative leading into the final season, Ogata is loyal only to himself and pursues the hidden Ainu gold for his own obscure reasons. After a falling out with Lieutenant Tsurumi, who had manipulated him, Ogata goes rogue and eventually forms a temporary alliance with Hijikata's group, acting as an independent agent caught between the various factions vying for the treasure. A key relationship that defines his role is his antagonistic rivalry with the protagonist, Saichi Sugimoto, whom he has repeatedly tried to kill. Another significant relationship is with Vasily, a Russian sniper he fought and severely wounded; Vasily survives and becomes obsessively dedicated to hunting Ogata, leading to a final confrontation between the two snipers. His connection to Tsurumi remains deeply personal and fraught with tension, as Tsurumi’s manipulations directly led to the destruction of his family.

Throughout the series, Ogata undergoes significant physical changes that reflect his journey. He suffers a horrific fall from a cliff while fighting Sugimoto, which results in two prominent scars on his face. Later, he is shot in the right eye by Asirpa's poisoned arrow, a wound that forces him to wear a bandage and eventually a prosthetic eye, permanently affecting his legendary sniping ability. Despite this loss, his development sees him becoming increasingly isolated and psychologically tormented by his inability to understand selfless love and compassion, which are embodied by characters like Asirpa and Sugimoto.

Ogata’s most notable ability is his extraordinary skill as a marksman. He prefers a Type 30 rifle for its long-distance accuracy and is capable of making precise shots at targets within 300 meters using only iron sights. He possesses immense mental fortitude, allowing him to remain perfectly still for long periods in harsh conditions, as well as sharp hearing to identify firearms by their sound. He is also fluent in Russian, a skill he keeps largely hidden and which sets him apart from many of his peers.