Myu, also known as Myu Nagumo, is a young Dagon girl who becomes Hajime Nagumo’s step-daughter after he rescues her and her mother, Remia, from slave traders. Remia’s subsequent marriage to Hajime integrates Myu into his family, where she is adopted by Hajime’s companions: Yue, Shea Haulia, Tio Klarus, Kaori Shirasaki, Shizuku Yaegashi, Aiko Hatayama, and Liliana, securing her place in their extended household.

Kind, obedient, and cheerful, Myu uplifts the group’s spirits through playful activities like impromptu bathing—occasionally still clothed—and open affection for her family. Yet she displays age-appropriate vulnerability, erupting into tantrums or tears when Hajime faces criticism, such as crying intensely over Kouki Amanogawa’s disparaging remarks until Hajime consoles her. Despite her youth, she bravely accompanies Hajime’s team on perilous missions, including the Orcus Labyrinth rescue.

Her character matures emotionally, notably when Hajime prepares to return to his original world. Though overwhelmed by sadness, she suppresses her tears to avoid burdening him, crafting clamshell necklaces as farewell gifts that embody her resilience. Myu also acts as a moral compass, urging Hajime to assist others and mediating conflicts among his admirers by voicing her dislike for their infighting.

Malapropisms punctuate her speech, most famously mislabeling Tio’s perversions as "Sexy Neglecting," a recurring quirk. Innate curiosity about the world and deep sympathy for others further define her narrative role.