Yosuke Itsuki (born Shinsuke Kimura) emerges as a morally complex freelance writer first entangled in the "Legend of Lake Hiren Murder Case." Initially characterized by ruthless opportunism, he callously pursues tragedies as literary fodder, even intruding on victims’ families for material. Surviving an attempt on his life during the Lake Hiren killings forces a reckoning with the human cost of his actions, gradually reshaping him into a more ethically conscious journalist.

His contentious dynamic with detective Hajime Kindaichi evolves into an uneasy partnership, with Itsuki repeatedly leveraging his network to draw the investigator into mysteries. This growth manifests in guarded empathy: he suppresses a coerced killer’s identity to shield their motives and withholds exploitative details of Lake Hiren’s tragedy, balancing journalistic ambition with newfound restraint.

A college dropout from Meiji University with ties to radical student movements—later retroactively adjusted in continuity—Itsuki ages from his early 30s to 50s across cases. His most defining arc intertwines with Hazuki Mogami; their combative rapport softens into mutual devotion, culminating in his fierce defense of her against murder charges. Her subsequent death fractures him emotionally, leaving lasting scars.

Though haunted by shadows of Lake Hiren’s perpetrator and residual trauma from other cases, Itsuki transforms from cynical outsider to Kindaichi’s strategic ally. His dual identity as a survivor of multiple plots and a writer attuned to human vulnerability positions him as a conduit between the detective’s logic and the raw, often tragic truths beneath each crime.