Miharu Ayase is one of the central characters in the story. She is the childhood friend of Amakawa Haruto, the person Rio was in his previous life. In her original world, she mysteriously disappeared right after their high school entrance ceremony, an event that deeply devastated Haruto and left him with the lifelong regret of never confessing his feelings to her. Miharu grew up as Haruto's next door neighbor, and their families were close. From a young age, she was considered cute and often attracted attention from boys, though this attention frequently manifested as teasing and bullying, with Haruto always stepping in to protect her. This protection fostered a deep sense of dependence on him and formed the foundation of their bond. When Haruto was forced to move away after his parents divorced, a devastated Miharu begged him to stay. He promised her that he would one day return and take her hand in marriage, a promise that became a guiding hope for both of them as they matured.

Miharu is a gentle, kindhearted girl, often described as being almost too kind for her own good. She is honest, responsible, and deeply loyal, holding onto promises from her childhood even years later. She is modest, caring, and prefers to stay in the background rather than be the center of attention. She was ranked first in her middle school on lists of girls the boys wanted to marry and of ideal housewife type girlfriends. Despite her popularity, she is naturally shy and reserved, particularly when interacting with boys. This shyness, combined with a forgiving disposition, sometimes makes her vulnerable to being taken advantage of. She is also known for being very good at cooking. After Haruto's departure, she remained close to Aki Sendo, Haruto's stepsister, and through her became acquainted with Aki's new siblings, Takahisa Sendo and Masato Sendo. Although Miharu still felt uneasy around boys, she made an effort to befriend Takahisa for Aki's sake.

Her motivation is deeply tied to her connection with Haruto and the promise they shared. She holds on to that bond even after being transported to a new world, and the desire to reunite and honor that connection drives her actions. She is also motivated by a desire to protect and care for those around her, especially the companions she traveled with. Her role in the story is significant as one of the main heroines. She is part of the group summoned to the fantasy world, along with Satsuki Sumeragi, Takahisa Sendo, Aki Sendo, and Masato Sendo. Shortly after their arrival, she was separated from the others and stranded in the wilderness with Aki and Masato. The group was briefly captured by slave merchants before being rescued by Rio. After the rescue, she and the others were taken to the Spirit Folk village, where they began to adapt to the new world.

Her key relationships include her deep and longstanding connection with Rio, who was Haruto in his past life. She is his first love, and their childhood promise of marriage is a central emotional pillar for both characters. When Rio hesitates to approach her initially due to a misunderstanding about her relationship with Takahisa, she remains unaware of his true identity for some time. She also has a strong bond with Satsuki Sumeragi, who was her senior and fellow student council member; their friendship deepened after their transportation to the other world. Her relationship with Takahisa Sendo is complicated. Takahisa developed feelings for her from the moment they met, and while Miharu made an effort to be comfortable around him for Aki's sake, the frequent interactions gave others the impression they were close, which contributed to Haruto's earlier misunderstanding.

Miharu's development over the course of the story involves her gradual adaptation to the fantasy world and her growth in confidence and capability. She begins as a gentle but vulnerable girl unfamiliar with the dangers of her new environment, and through her experiences and training, she becomes more capable of protecting herself. A notable aspect of her development is her exploration of her own innate abilities. As a summoned individual, she possesses an unusually vast amount of magic essence, far greater than most natives of the new world, though her inexperience leaves much of her potential untapped. For her own safety, she undergoes basic martial arts training under Rio's guidance, learning to wield a staff for self defense. She also begins learning spirit arts, and thanks to a brief bond with the spirit Aishia, her affinity for spirit arts is significantly enhanced, surpassing even the highest level practitioners among the Spirit Folk. This grants her the potential to become an exceptionally skilled spirit user, though her gentle nature keeps her focus on supportive rather than combative roles, and her techniques are designed for protection rather than offense.