Hiromi Ishimaru

Hiromi is, officially, Makoto's cousin. After her father died, she was adopted by her mother, the daughter of Makoto's grandfather, meaning that she and Makoto are actually not related by blood. Hiromi and Makoto knew each as young children, when Makoto was believed to be a boy, causing Hiromi some surprise when she meets Makoto as a teenager. After Makoto reveals her secret, Hiromi becomes Makoto's protector and tutor. She tries to protect Makoto's secret and steer her away from harm, but inevitably gets caught up in Makoto's entanglements.
(source: Wikipedia)