Jirou Tomitake is a freelance photographer who frequently visits the rural village of Hinamizawa. On the surface, he travels from Tokyo several times a year, claiming his purpose is to photograph wild birds and capture the village's scenery across all four seasons. Known for his muscular build, brown cap, green sleeveless shirt, and the camera he always carries, he is a familiar and well-regarded figure among the villagers. He is on friendly terms with the local children, particularly Mion Sonozaki and Rena Ryugu, who affectionately refer to him by the nickname Tommy.

Despite his harmless public persona, Tomitake's true identity is far more complex. He is a First Lieutenant in the Japan Self-Defense Forces and a former sniper instructor who was reassigned after an eye injury. Recruited by a secretive government organization known as Tokyo, his real mission is to serve as an auditor for the Irie Clinic, a research facility studying the mysterious Hinamizawa Syndrome. Using his photographer cover, he monitors the clinic's progress, manages its budget, and acts as a liaison, reporting his findings back to his handlers. He also has the authority to request backup from a special forces unit called the Bloodhounds.

In his interactions with others, Tomitake is generally calm, gentle, and easygoing. He rarely displays anger and is well-liked for his polite and earnest nature. However, he is also somewhat socially awkward, particularly around women, which can lead to moments of unintended comedy. He has a noted fondness for nurse uniforms, a quirk that is often a source of lighthearted embarrassment.

His most significant relationship is with Miyo Takano, the head researcher at the Irie Clinic. He is romantically interested in her and frequently asks her on dates, offering her photography lessons as a pretext for spending time together. He genuinely cares for her and wishes to be the person who supports her and eases her loneliness. For her part, Takano plays along with his advances, and the two are often seen together as a couple. This relationship is deeply complicated, as he is simultaneously her lover and her government-mandated supervisor.

Across most of the story's arcs, Tomitake meets a grim and predictable fate. He is found dead on the night of the annual Watanagashi Festival, having clawed his own throat out in a state of madness. This event is so consistent that it has earned him the nickname "Time Signal" among fans. The cause of his death is eventually revealed to be a murder orchestrated by Takano, who secretly injects him with a drug that induces Level 5 Hinamizawa Syndrome, triggering the fatal delusion. He is an unwitting victim in her larger plan to trigger a catastrophic event known as the Great Hinamizawa Disaster.

Tomitake is not without his own formidable abilities. His military training has made him an expert marksman, capable of precision shooting even from a moving vehicle. He is also skilled in lock-picking, a talent he demonstrates when he nonchalantly opens the lock to the village's forbidden ritual storehouse. These skills, along with his knowledge of counter-intelligence, make him a dangerous operative when the situation demands it.

The character's development culminates in the final story arc, Matsuribayashi-hen. Forewarned by Furude Rika, he manages to avoid the trap that usually kills him. With this advanced knowledge, he uses his authority to investigate Takano, uncovering her embezzlement and her alliance with a rogue paramilitary group. Refusing to be a part of her conspiracy, he instead works with Rika's allies to stop her. In the climax, he confronts Takano, recognizing that she herself is suffering from advanced Hinamizawa Syndrome. Instead of condemning her, he chooses to forgive her and helps to save her from her own madness, offering her a chance for redemption and a new life. In this arc, his role evolves from a passive victim into an active and crucial force for resolving the tragedy of Hinamizawa.