Height 155 cm Izumi Shimomura is an Ajin. Her name is taken from her birth father's last name (Shimomura) and her mother's maiden name (Izumi). Her former name was Yoko Tainaka. Izumi is a rather quiet and reserved individual, talking mainly when informing Tosaki about something. Her answers are usually short and to the point. Even though she is an Ajin, she chose to live between humans in secret and doesn't seem to be consumed completely by resentment towards humans despite her background. She seems to be quite intelligent and understanding, both towards Tosaki and when interrogating Nagai Kei's younger sister, Eriko. However, despite her initial stoic appearance, she can get embarrassed easily (for example when she said too much to Eriko and when Tosaki commented on her casual clothes).

Spoiler

Due to her past trauma caused by both of her parents and love life, she became very depressed and suicidal, often cutting herself and eventually ends up attempting suicide.