Ken Yamamura serves as the secretary of 315 Production, where he also functions as a tutorial guide and provides information to the producer. His exact age is not stated, though his manner of addressing other characters suggests he is likely a young adult. Born on July 2nd, he is a native of Kanagawa Prefecture. Standing at 176 centimeters tall and weighing 61 kilograms, he has a lean build. He has green hair, brown eyes, and is frequently seen wearing red-framed glasses pushed up on his head. His blood type is A, his hobby is fishing, and he possesses a skill for mental arithmetic. He is ambidextrous.

Ken is known for being a friendly and earnest individual who works diligently behind the scenes. His primary motivation is to support the idols and the producer, handling a significant amount of administrative work. However, he is also characterized as being quite clumsy. He often makes mistakes, such as spilling drinks on important documents, but his sincere and hardworking nature has earned him the trust of the idols at the agency. This reputation for mishaps originated in fan culture following server issues at the launch of a game, and this trait was subsequently incorporated into his official character.

In his role, Ken is the primary non-idol staff member seen assisting the producer. He is responsible for lesson support, managing schedules, and handling various office tasks to ensure the idols can focus on their performances. While his direct interactions with individual idols are primarily professional, he addresses them with appropriate honorifics, using -kun for those younger than himself and -san for those older, which has led to speculation about his age. He is not an idol himself but a dedicated administrative professional. His development throughout the series is subtle, as he consistently grows more reliable and experienced in his secretarial duties, becoming an indispensable part of the agency's daily operations.