Keiichiro Tachibana is the owner of the small bakery called Antique, where he also works as a waiter. He comes from an immensely wealthy and powerful family, being the grandson of the head of the Shirai Group, a major conglomerate. Despite his privileged upbringing, Keiichiro is a man of remarkable ability, having graduated from the prestigious University of Tokyo. He passed the Foreign Service Examination during his third year of university and the Bar Examination in his fourth year, demonstrating an exceptional intellect. Fluent in five languages including French, he was a top-performing salesman at a first-class trading company before abruptly leaving that successful career to open his cake shop.

Keiichiro has a complex and somewhat contradictory personality. Outwardly, he presents the image of a cheerful and charismatic shop owner, skilled at charming customers and particularly fond of looking at women. However, this smile often serves as a mask for a much darker interior. He is deeply marked by a traumatic event from his childhood when he was kidnapped by a man who was never apprehended. During his captivity, his abductor fed him cake every day, and as a direct result of this experience, Keiichiro has a strong aversion to all sweets, a bitter irony for a bakery owner. The kidnapping left him with recurring nightmares and significant psychological scars; for a long time, he could not stand being touched by older men, a phobia linked to his abductor. He acts as a Stepford Smiler, playing the role of the good and carefree son and boss to keep his family and friends from worrying about him, while internally he remains fractured by his past.

His core motivation for opening Antique is directly tied to his unresolved trauma. Despite his hatred for cake, he establishes a bakery as a way to lure out the man who kidnapped him twenty-eight years prior. He believes that by creating a shop renowned for its cake, his abductor, who loves sweets, might eventually become a customer. This is his method of confronting a past that continues to haunt him, as he seeks closure from the man who stole his childhood.

In the story, Keiichiro is the central figure around whom the bakery and its staff revolve. His role is both that of a capable manager, who handles customer service and the business side of things, and the emotional anchor for the group of broken men he has assembled. His primary relationships are with his three employees. The first is Yusuke Ono, a brilliant patissier who was Keiichiro's classmate in high school. Their history is fraught with tension, as Keiichiro once furiously rejected a love confession from Ono, telling him to die. This rejection had a profound and lasting effect on Ono's life. In their adult lives, Keiichiro is the one man who remains immune to Ono's "demonic charm," and their relationship evolves into a vitriolic but deeply accepting friendship built on a shared past and mutual need for atonement. The second key relationship is with Chikage Kobayakawa, his childhood friend and the son of his family's live-in housekeeper. Chikage was sent by the Tachibana family to look after Keiichiro and serves as a loyal, if somewhat clumsy, waiter. Chikage calls him "Young Master," and the two share a deep, unspoken bond as Heterosexual Life-Partners, with Chikage often being the one to comfort Keiichiro after his nightmares. The third employee is Eiji Kanda, a former professional boxer and ex-punk who becomes an apprentice to Ono. Keiichiro acts as a gruff but caring mentor to the much younger Eiji.

Throughout the series, Keiichiro experiences subtle but significant development. He begins to move past the guilt he feels for his harsh treatment of Ono in high school, learning to accept and work alongside him. He also starts to shed some of the protective shells he has built around himself, allowing his genuine care for his found family at the bakery to show more openly. His primary conflict of confronting his kidnapper remains a driving force, and the story follows his ongoing struggle to reclaim his sense of self and finally feel whole.

Keiichiro possesses a wide range of notable abilities beyond his business acumen. He is a natural all-rounder in sports, an expert at billiards, and skilled at card and board games. He is an excellent cook, capable of preparing both Japanese and Western dishes, and he has a talent for singing. Despite his personal dislike for cake, he has a hidden talent for making it; the one time he attempted to bake a cake, his first try was of a professional quality. His true expertise, however, lies in his memory, customer service, and the perfect sales smile he uses to run his antique shop.