Yoshiyuki Hatori holds the position of second editor-in-chief at Marukawa Publishing's Emerald shoujo manga department, recognized as one of its most skilled editors. His professional duties involve managing authors, primarily focusing on his childhood friend, popular mangaka Chiaki Yoshino, who uses the pen name Chiharu Yoshikawa. Hatori specifically chose editing as a career to stay close to and support Chiaki, fulfilling a promise made during their university years to always care for him.

Professionally, Hatori maintains a consistently serious, calm, and no-nonsense demeanor, earning respect for his punctuality, work ethic, and reliability. He demonstrates a helpful attitude towards colleagues, notably offering guidance to newcomer Ritsu Onodera about workplace dynamics and Masamune Takano. Beneath this reserved exterior lies deep loyalty and protectiveness, particularly towards Chiaki. He exhibits jealousy concerning Chiaki's other childhood friend and assistant, Yuu Yanase, stemming from a longstanding rivalry over Chiaki's affections that began in middle school when both recognized their romantic feelings. They maintain superficial civility for Chiaki's sake.

Hatori's personal history with Chiaki Yoshino forms his core development. Having known each other since childhood, Hatori harbored unspoken romantic feelings for years. A critical turning point occurred when Hatori kissed Chiaki without consent during his sleep, driven by an inability to suppress his emotions. This act triggered significant guilt, leading Hatori to resign as Chiaki's editor and contemplate exiting his life. However, Chiaki's subsequent panic and insistence on testing their romantic compatibility initiated their relationship. Despite ongoing misunderstandings, including the complication of Yuu, their bond strengthens through communication. Hatori occasionally struggles with self-doubt, fearing Chiaki mistook friendship for love, though Chiaki consistently reaffirms his genuine romantic commitment.

Domesticity defines their relationship dynamic, earning the fan label "Domestica" due to Hatori's extensive caretaking role. He regularly cooks, cleans, and manages Chiaki's household, compensating for Chiaki's focus on manga deadlines. This aspect is highlighted when Chiaki, after parental pressure about marriage during a family visit, casually suggests marrying Hatori following a wedding they attended. The statement visibly stresses Hatori due to its implications, though Chiaki clarifies he genuinely wouldn't mind that outcome, underscoring the relationship's progression and ongoing negotiations around commitment.

Background details reveal Hatori was shorter than Chiaki as a child, experienced popularity with women in high school (including being voted "best couple" with Sanae Hoshino at a cultural festival), dislikes sweet foods, and is an only child. His nickname "Tori" (meaning "bird") stems from his surname. He transitioned from using Chiaki's first name in childhood to his surname in adulthood, reflecting their evolving relationship.