Mayu Asamura is the older sister of Kengo Asamura. She has waist-length brown hair, which is naturally black but dyed brown, and brown eyes. Her typical attire includes a white jacket and a black lace-trimmed t-shirt, along with a purple accessory. She works in an office environment, though she finds her colleagues uninteresting, which often leads her to drink alcohol after work. Mayu's most prominent trait is her intense obsession with handsome men; she becomes flirtatious and even delusional when encountering attractive individuals. Despite this, she genuinely cares for her younger brother Kengo and shows concern for his well-being.

Mayu was trained by a figure known as Master in the art of exorcising evil spirits, granting her the ability to combat supernatural threats. Her role in the story is largely that of a supporting character who occasionally becomes involved in the main conflict. At one point, she is possessed by a kokuchi, a parasitic shadow spirit, but is rescued by Kengo and the protagonist Akira. During this incident, she regains her senses and demonstrates her protective feelings toward her brother. She also possesses the unusual ability to see Shirogane, a mysterious being from the shadow world, for reasons that are not fully explained. Mayu's motivations are driven by her attraction to good-looking men and her loyalty to her family. Her development is subtle but includes moments where her superficial interests give way to genuine emotional connections. Her exorcism abilities, while learned from Master, are not depicted as extensive or frequently used in battle. Overall, Mayu serves as a comic relief character whose underlying affection for her brother anchors her place in the narrative.