A boy whose family was killed one year before the series' start, including his father, mother and step-sister Aiwa. In exchange for help to find the culprit behind the murder, Mahiro agrees with Hakase's plan to stop the resurrection of the Tree of Zetsuen with Yoshino's help. With little care for the destiny of the world, Mahiro's only desire is to locate and kill the murderer of his family, especially for Aiwa's sake. Despite not being related by blood with Aiwa, Mahiro claims he never had any romantic feelings for her, despite his actions imply otherwise.
Mahiro's setup and behavior includes allusions to Prince Hamlet, as just like the main character from Shakespeare's tragedy Hamlet, he is prone to abandon all morals and reason for the sake of enacting his revenge.
Information Source: Wikipedia