Detective Ryо̄ Hoshino operates within Tokyo Metropolitan Police Department’s Criminal Investigation Division 1. He demonstrates a serious, dedicated approach to duties, strictly adhering to hierarchical structures and following superiors’ orders without contradiction. Physically, he possesses brown hair, lilac-colored eyes, and stands 171 centimeters tall.

Personality assessments define him as orderly, structured, and rule-abiding, driven by a strong sense of responsibility and duty. His methodical work prioritizes meticulous evidence gathering and data analysis, favoring concrete facts over emotional considerations. Socially reserved, he maintains emotional distance, reflecting introversion and analytical detachment. Symbolic interpretations link him to a heart motif representing devotion to authority and institutional obedience; this symbol frequently appears near his head to signify its connection to his mindset.

His professional history includes a past partnership with Haru Katō, strained by undisclosed circumstances preceding the series. This creates underlying tension in their interactions. Within Division 1, he collaborates with colleagues who acknowledge his competence. Symbolic analysis of official artwork designates him the "white rabbit," embodying constant motion and urgent dedication to responsibilities, reinforcing his lawful-good alignment and relentless professional focus. Throughout appearances, he remains a secondary character consistently embodying institutional loyalty and methodological policing.