Izumi Shimomura is a pivotal character in the anime series 'Ajin: Demi-Human.' She serves as an assistant to Yu Tosaki, a government official involved in the management and control of Ajin, beings with immortality. Despite her stoic demeanor, Izumi's character is complex, marked by loyalty and resilience. She is an Ajin herself and uses her abilities to protect Yu and accomplish their goals. Her backstory and development highlight themes of identity and morality, making her an intriguing figure in the narrative.