Yuji Tachiki, a Great Dane beastman and investigator for the Anima City Police Department, balances human and beastman forms with equal precision. His human appearance features a light tan complexion, a prominent dark gray mustache, and thick eyebrows, complemented by a gray suit, mint turquoise tie, light olive overcoat, and purple-gray newsboy cap. In beastman form, his attire remains unchanged, though his physique shifts to dark gray fur, a black nose, droopy snout, and floppy ears—mirroring his canine lineage. His name, rooted in "standing tree" and the union of "courage" and "sequence," reflects a personality marked by quiet resolve and methodical action.

A steadfast advocate for protocol, Yuji thrives in fieldwork, meticulously gathering evidence and pursuing leads with calm persistence. His investigations often intersect with Shirou Ogami, whose impulsive interventions force Yuji to secure chaotic scenes, such as recovering orphaned children after the Rabbit Town trafficking case. Though professionally respectful toward Shirou, tensions simmer when pursuits end in frustration, as seen after a medical center attack where Yuji’s efforts to detain him falter.

Yuji’s rigid adherence to procedure sometimes backfires, notably during the Ginro sect incident. Permitting a preacher’s visit to the detained Yaba unwittingly facilitates the latter’s feral transformation and escape, resulting in bureaucratic repercussions like mandatory daily reports. His principles face further strain when Giuliano Flip’s paramilitary group employs reckless firepower against Sylvasta’s forces, provoking Yuji to condemn their disregard for restraint.

While his personal history remains undisclosed, Yuji’s identity remains anchored to his role, navigating Anima City’s fractured society through unyielding dedication to justice—even as systemic inefficiencies and moral ambiguities test his resolve.