Yūsei Shirosaki is a 34-year-old man from Akita Prefecture, where his family farms rice. His older brother once shared his home but moved to the United States, freeing up a room later occupied by Kentarō Momose. Shirosaki stands 1.81 meters tall with a slim build, ochre-colored eyes, and ashy blond hair. Professionally, he slicks his hair back, though one strand habitually escapes; at home, he wears it down, often sporting significant bed-head in the mornings. His cat-like eyes inadvertently terrify felines, who perceive him as a monster. For work, he favors a gray suit paired with a baby pink or white shirt and varied ties. As chief of the Planning and Sales department at Minette advertising agency, Shirosaki exhibits excellent concentration and performance, prioritizing a pleasant work environment and believing in job enjoyment. Outside work, he appears airheaded and easily distracted. His defining trait is a natural goofiness, leading to unintentional antics like buying menstrual cramp medicine for Momose's stomachache or publicly handing over house keys in a manner mistaken for a marriage proposal. He frequently uses self-deprecating humorous stories about his clumsiness to ease workplace tension, his actions always stemming from genuine care. Shirosaki demonstrates deep empathy, especially towards subordinates with past workplace trauma. He rushed to fetch medicine when Momose suffered a health episode, accidentally cracking his phone screen; he chose not to repair it as a reminder of Momose's efforts. When Momose faced stalking from a former boss, Shirosaki immediately offered him the vacant room. He adopted an abandoned cat named Hakutō, who had fled "power harassment" from a previous owner. Despite cats generally fearing him, Shirosaki bonded with Hakutō and communicated understanding of the cat's perspective. Childhood experiences left him with an irrational fear of gas storage containers, which he imagined as dinosaur eggs poised to hatch and endanger people, and a lasting terror of ghost stories after being traumatized by a local festival demon. He displays artistic skill through frequent doodling, used for both conceptual work and cheering up colleagues. His grandmother is a notable YouTuber, and his birthday is February 22. His surname combines "white" (白) and "cape/peninsula" (崎), while his given name means "excellence/gentleness" (優) and "clear/pure" (清).