Izumi Curtis, born Izumi Harnet, the teacher of Ed and Alphonse Elric, agreed to train the brothers to hone their alchemical abilities after their mother died. She expands their training with a regimen of philosophy, martial arts, and living off the land. Her methods are derived from her own alchemy training: in the manga and second anime, she was forced to survive in the northern region surrounding Briggs Fortress for a month (although it turns out she succeeded by stealing supplies from the northern fortress), whereas in the first anime she was taught by Dante. She thinks of the Elrics as her own sons, and although she severs her student-teacher ties with them after learning of their attempts with human transmutation (and similarly Ed's joining the State Military), she continues to do all she can to help them. She can be quite violent when punishing or sparring with the Elric brothers, so they tend to be deathly afraid of her. Her claim of "I'm a housewife!" while confronting Greed was a favorite scene of Arakawa's to draw.

Izumi and her husband Sig Curtis (シグ・カーティス, Shigu Kātisu) were expecting a child years before the start of the series; however, their son was stillborn. Izumi tried and failed to revive the child through human transmutation (an act that created Wrath in the first anime). The failed attempt took some of her internal organs, resulting in infertility, and causing her to periodically cough up blood. Izumi gained the ability to use alchemy without a transmutation circle after seeing the "truth."

In the manga, Izumi attracts the attention of the State Military for surviving the failed human transmutation. As she and her husband travel around Amestris in order to avoid the military, they eventually meet Ed and Al's father Hohenheim. He rearranges her insides to ease the blood flow, and persuades her to help collaborate in bringing down the State Military.