Haruhiro is the central character and protagonist of his story, a young man who awakens in the unfamiliar world of Grimgar with no memories of his past life except for his own name. He is depicted as having an unremarkable stature and an average build, a physical ordinariness that is mirrored in his self-perception as a deeply mediocre individual. His most distinctive physical trait is his sleepy-looking eyes, a feature that earns him the nickname Old Cat from his instructors at the thieves guild.

In terms of personality, Haruhiro is initially presented as somewhat awkward, indecisive, and lacking in self-confidence. He is strongly aware of his own averageness and often worries about the future, carrying a significant inferiority complex. Despite this, his nature is fundamentally good and grounded in common sense, with a deep-seated care for his comrades. He is portrayed as a listener rather than a talker, someone who observes the people around him closely. While he frequently experiences fear, especially in combat, he consistently finds the resolve to rouse himself and take action. Over time, his experiences force him to mature from a hesitant and unreliable figure into a more dependable individual who learns to show understanding and empathy for his companions.

Haruhiro's primary motivation is the survival and protection of his party. After being thrust into the deadly world of Grimgar, he and his fellow amnesiacs must form a volunteer soldier party simply to earn a living and avoid death. His driving force evolves from basic survival to a powerful protective instinct, as he comes to regard his party as a surrogate family with whom he shares irreplaceable bonds. He is not driven by glory or the desire to be a hero, but by the quiet determination to keep his friends safe and maintain the unity of the group, a goal he consistently prioritizes above all else.

His role in the story is defined by his position as the party's thief and its reluctant leader. Following the tragic death of Manato, the group's original charismatic leader, Haruhiro is forced to assume command out of necessity, despite his profound self-doubt and grief. This transition is a central pillar of his character development. As a thief, his role in combat is to function as the team's scout, using stealth to locate enemies and map terrain before reporting back, and to provide flank support with his daggers or execute surprise attacks from behind. His leadership style is collaborative and strategic rather than authoritarian, focusing on fostering input and cooperation from his party members.

Key relationships profoundly shape Haruhiro's journey. The death of Manato is the most significant event, leaving a permanent scar and forcing him to grow into a leadership role he never wanted. His relationship with Mary, a priest who joins the party after Manato's death, is complex; she is initially cold and distant, challenging the team's cohesion, but Haruhiro persists in trying to understand her, and he eventually develops romantic feelings for her. He shares a close bond with Yume, a hunter in the party, and a pivotal moment in their grieving process involves a shared embrace that helps them both confront the loss of Manato, hinting at a deep, if unspoken, connection. His relationship with the volatile Ranta is often tense, marked by arguments, yet they remain bound together as members of the same struggling party.

Haruhiro's development is a slow, realistic progression from weakness to strength. He begins as a cowardly and shy individual, but through relentless hardship and loss, he gradually builds willpower and courage. He learns to make difficult decisions for the good of the group, transitioning from a passive follower to a reliable anchor, all while retaining his introspective and cautious nature. His arc is not about becoming an invincible hero, but about forging resilience and dependability from a foundation of fear and insecurity.

In terms of notable abilities, Haruhiro is a skilled thief, though his talents are grounded in realism rather than superhuman prowess. He is trained in a variety of techniques such as Stealth Walk for silent movement, Backstab for delivering massive damage from behind, and Widow Maker, a grappling technique used to immobilize and dispatch an opponent. He also possesses practical skills like lock-picking. His most remarkable and rare ability is called the Gleaming Line. This mysterious skill allows him to occasionally perceive a line of light that reveals a fatal weak point on an enemy; when he follows this line with his blade, it can result in a near-instant kill. However, this ability is unpredictable and not something he can control or rely upon at will. While his combat abilities grow, the source of his greatest strength lies in his observation, his judgment in critical moments, and his unwavering commitment to his party's survival rather than in any exceptional innate talent.