Yuki Karuizawa holds the position of executive secretary at Mujina Company. She orchestrates the child CEO's schedule and professional duties, managing substantive company operations and logistical coordination. Her pragmatic adult oversight provides a necessary counterbalance to the CEO's unconventional leadership style. Her past as an orphan, having lost her parents before her career began, informs her background. Visually, she is defined by her glasses and professional attire, reflecting her corporate function.

Her responsibilities extend to supervising employees such as Mayu Warito and Garcia Dekasegi. She constantly navigates workplace turbulence caused by the CEO's juvenile behavior, a core task that involves translating youthful directives into actionable business plans and mitigating ensuing complications. Her narrative function is consistent across all animated iterations, including the original net animation and its sequel season, maintaining her established backstory and professional capacity. Her interactions consistently showcase her patient management of executive whims while ensuring smooth organizational flow.