Kazuki's sister and a first-year student at the same school. Mahiro is scatterbrained and perpetually cheerful, often lacking common sense. She sees nothing wrong with lending her brother her gym clothes for school. Her quirks and personality are so similar to Kazuki's that no one questions their relation, even though they don't look alike. She secretly hopes that Tokiko and Kazuki will marry, making Tokiko her new sister.
Mahiro learns that her brother is an alchemist warrior when the LXE launch a large-scale attack on the school. She understands that Kazuki occasionally has to go on missions. However, she decides not to pry into the details of his activities as an alchemist warrior.
