Yūji Tachiki, a Great Dane beastman and investigator for the Anima City Police, sports a light tan complexion in human form, paired with a prominent dark gray mustache, thick brows, and a wardrobe blending professionalism with muted flair: a gray suit, mint turquoise tie, light olive overcoat, and purple-gray newsboy cap. His beastman form mirrors this attire, complemented by dark gray fur, a black nose, drooping ears, and a sagging snout.

Calm and methodical, he approaches investigations with methodical seriousness, prioritizing protocol above haste. His thorough on-foot diligence often leads him to crime scenes after critical moments conclude. In a human trafficking case resolved by an external intervener, he shifts focus to securing affected children’s relocation, balancing gratitude with duty.

During a Sylvasta Farmaceuticals bomb threat, he teams with colleagues to neutralize explosives and pursue suspects. Facing accomplices, he deploys calculated questioning to expose guilt, though they evade capture. At a medical center attack, he reacts with measured surprise to sabotage claims and joins the chase as the suspect flees.

Interactions underscore his unyielding adherence to protocol. He grants a Ginro sect figure access to a detainee, trusting their intent, yet unwittingly facilitates an escape—a misstep spawning repeated reports to superiors. Confronting armed groups, he condemns reckless weapon use, stressing respect for legal limits.

His name reflects his essence: "Tachiki" (立木), meaning "standing tree," embodies unwavering principles, while "Yūji" (勇次)—"courage" and "sequence"—hints at reserved bravery surfacing when duty demands. No records detail his pre-police history or extracurricular engagements beyond documented cases.