Mutsumi appears in the anime Seven of Seven as a supporting character known as Examinee 623 and the host of his own radio program. He is a quiet and reserved young boy with a deep love for music and technology. His passion for music is a defining trait; he works as a DJ, creating and mixing tracks that allow him to express his emotions and cope with challenges. He is introspective and analytical, often lost in thought or focused on his technical projects. Mutsumi is a childhood friend of the main character, Nana Suzuki, and uses his skills to support her and the six other Nanas that result from her split personality. He helps them overcome obstacles by operating equipment and composing music tailored to their needs. His role in the story is primarily that of a reliable and resourceful ally who offers quiet assistance from the sidelines. Mutsumi is motivated by a desire to connect with others through his art and to use his talents to aid his friends. While he does not undergo significant personal development over the course of the series, he remains a steady and supportive presence. His notable abilities include expert DJing, technical proficiency with audio and electronic devices, and a keen understanding of how music can influence mood and situation.