Habutae Masamune operates as a Human Analyst within the Kura organization’s Wellside division, tasked with identifying and reporting on individuals encountered in id wells—fractured mental planes of serial killers. Having joined Kura six months before the series’ events, he collaborates with colleagues like Akihito Narihisago and the Brilliant Detective Sakaido to analyze cognitive data extracted during investigations.

His appearance includes spiky black hair, brown eyes, and a professional wardrobe dominated by a black suit paired with a light pink shirt and darker pink tie. For formal events such as funerals, he shifts to a dark-toned suit, white shirt, and black tie, adhering to situational expectations.

Personally disciplined and focused, he approaches his duties with measured seriousness, though he occasionally reveals dry amusement, such as when countering Sakaido’s speculative tactics. He acknowledges the speculative, "sci-fi" nature of Kura’s technology while demonstrating empathy in interpreting others’ motivations, proposing altruistic rationales for certain id wells. Less emotionally driven than peers like Kazuo Wakashika, he balances professionalism with compassion, finding overtly abrasive behavior unsettling.

His background prior to Kura remains undisclosed, with his narrative role centered on operational support rather than personal development. He maintains pragmatic reservations about the organization’s reliance on former criminals for id well exploration, reflecting cautious skepticism toward their methods.

The name "Masamune" blends the characters for "proper" and "religion," while "Habutae" originates from terms meaning "feather," "two," and "multilayered"—etymological nuances not directly reflected in his characterization. His role remains confined to the primary series’ investigative framework, with no documented expansions into spin-offs or other media.