Keiichirō Shinozaki serves as the dedicated personal secretary to Madoka Takatori, a position he has held since childhood, having grown up alongside Madoka as well as the young Chiyo and Miyako. His role is fundamentally that of a caretaker and manager, ensuring that the eccentric Madoka adheres to his professional schedule and completes his costume design work on time. Keiichirō is a composed, capable, and disciplined individual who presents a serious and no-nonsense exterior. He is often seen scolding Madoka for his lazy habits, his tendency to make a mess, and his habit of bringing stray cats into the house, despite being allergic to them.

Despite his stern demeanor, Keiichirō possesses a genuine kindness and treats Chihiro Komiya, Madoka’s young nephew and newly appointed live-in maid, with consistent warmth and respect. He shares a strong rapport with Chihiro, recognizing the boy's own serious, hard-working, and mature nature. In many ways, Keiichirō acts as a second parent or an older brother figure to Chihiro, supporting him and ensuring Madoka fulfills his responsibilities as a guardian and employer. He becomes a trusted confidant and a steady, reliable presence in Chihiro's new life.

One of his primary motivations is to manage the chaos that often surrounds Madoka, keeping the household and business affairs running smoothly. He dislikes Madoka's eccentricity and laziness, which constantly test his patience. He is highly effective in his role, not afraid to use subtle, strategic methods to achieve his goals, such as leveraging Madoka’s embarrassing cross-dressing photographs as persuasion to ensure deadlines are met. This reveals a pragmatic, and slightly scheming, side to his personality.

Beneath his professional and unflappable composure, Keiichirō harbors a few notable quirks and secrets. He is domestically hopeless, a fact that left Madoka's mansion in considerable disarray before Chihiro arrived to take over the housekeeping. He also has a soft spot for cats, secretly keeping one named Kuromame, a fact he must carefully hide from the allergic Madoka. He loves sushi and has a particular fondness for pudding, a fact that another character, Miyako Ōtori, knows and uses to try and win his affection. In his relationships, he remains seemingly oblivious, or perhaps feigns ignorance, to the romantic feelings Miyako holds for him, while maintaining a professional and cordial rapport with her.