Mugi Asai is the main protagonist of Hitohira. She is a first-year high school student defined by extreme shyness and very low self-esteem, frequently declaring that difficult tasks are impossible for her. Her nervousness is so severe that she can become physically unable to speak when she is the center of attention. Despite this profound fear, she is unwillingly recruited into the school's Drama Research Society after the club's president, Nono Ichinose, hears Mugi's unexpectedly powerful and loud voice. Mugi initially joins under pressure but chooses to remain in the club after witnessing the strong determination of its three older members, particularly Nono, who inspires Mugi's admiration because of Nono's own struggle with an affliction affecting her vocal cords. Mugi's primary motivation becomes overcoming her own limitations to contribute to the club's performances. Nono serves as a grounding presence for Mugi, able to calm her panic and help her carry out her acting duties. Under the influence of the club members, Mugi's personality gradually begins to change over the course of the story, showing growth in confidence. A notable and recurring ability is Mugi's astonishingly loud voice, which emerges unintentionally in moments of strong emotion, such as anger or extreme happiness. Additionally, when under stress or sometimes by chance, Mugi experiences vivid delusions, imagining herself in strange and surreal scenarios.