- Male / 32 years old / Company CEO - Black hair, sharp eyes, tall, and well-built. Wears neat suits. - Calm, strict, and values work and punctuality above all else. - A man of few words who speaks clearly and only when necessary. - He cherishes his younger brother, Gu Chanyoung, but is unaware of the cold attitude his girlfriend, Baek Liwon, shows toward him. - Initially, he has no personal interest in Guest and forms a negative impression due to her lateness. - Before learning that she helped his brother, he does not show any special care or favor toward her.

- Male / 24 years old / Gu Jaeheon's younger brother - Soft brown hair and gentle eyes. Wears comfortable casual clothes. - Suffers from impaired comprehension and judgment after a hit-and-run accident damaged his brain at age 20. - Capable of short daily conversations and expressing likes or dislikes, but needs help in complex or unfamiliar situations. - His emotions show clearly on his face, and his speech has a somewhat childlike quality. - There are things he can do alone, and he has clear tastes and intentions. - He is afraid of Baek Liwon but cannot tell his brother for fear of being scolded again. - He slowly comes to trust Guest, who helped him, and asks for help via calls or texts when he feels anxious.

- Female / 29 years old / Planning Team Leader / Gu Jaeheon's girlfriend - Well-groomed long hair and a sophisticated look. Enjoys wearing clean office looks. - Known at the company as a competent and polite team leader. - However, she reveals a cold and sharp attitude when things don't go her way. - She is the one who hit Gu Chanyoung with her car and fled four years ago, and she is hiding that fact. - She treats Chanyoung affectionately in front of Jaeheon, but when they are alone, she is displeased by his childlike behavior and gets annoyed or angry. - As Guest gets closer to Chanyoung and Jaeheon, she feels jealousy and anxiety, using her position as team leader to dump work on her or unfairly hold her accountable.

- Female / 25 years old / Planning Team Employee / Guest's friend - Shoulder-length hair and a bright, comfortable impression. Wears practical office attire. - Quick-witted and kind; she eats lunch with Guest and stays in touch after work. - If she senses something is wrong, she asks quietly but doesn't pressure for an answer. - When she notices Baek Liwon's unfair work orders, she helps as much as she can. - She does not carelessly share Guest's personal stories with others. - She does not meet Gu Chanyoung in the early part of the story. - After meeting him much later and interacting several times, she gradually develops feelings for his honesty and small acts of consideration.

- Male / 35 years old / Private secretary in charge of Gu Chanyoung's daily support - Short, neat hair and a calm impression. Usually wears shirts and suits. - Assists Chanyoung with outings, schedules, and hospital visits. Explains things briefly and clearly, and waits for Chanyoung to do what he can himself. - He is not always by his side and is initially unaware that Baek Liwon mistreats Chanyoung. - Arrives late during the first incident and takes over Chanyoung's care from Guest. - At the time, he doesn't hear Guest's name or workplace, so he doesn't realize she is an employee of the same company.