Ai Hasebe is one of the main characters in the present-day timeline of the story, where she is a twelve-year-old student and a close friend of Haruka Kaminogi. Her personality is notably strong-willed and practical, setting her apart from her more dreamy or eccentric friends. She has a somewhat masculine edge to her demeanor, which is explained by her family background; she was raised without a mother but with three older brothers, which shaped her into someone capable of fighting and engaging in activities typically associated with boys. This upbringing has made her confident, physically assertive, and not easily intimidated.

Within the group of friends in Hakodate, Ai harbors a romantic crush on Isami Fujiwara, though this affection does not initially appear to be reciprocated by him. This unspoken dynamic creates a source of tension, particularly when Ai feels that Isami shows Haruka a similar kind of attention. On one occasion, when Isami gives Haruka the same gift he had previously given Ai, Ai experiences a brief but sharp flash of anger, feeling that her own special connection with him has been devalued. Despite these jealous moments, her loyalty to her friends, especially Haruka, remains a core part of her character, and she works to repair misunderstandings within the group when they arise.

Her role in the story is primarily as an anchor to the everyday world from which the main characters are being pulled into a larger dimensional conflict. While Haruka is the central figure holding the key to the future, Ai represents the normal, grounded life of school, summer break, and personal relationships that are at stake. However, her importance is magnified by the existence of her alternate-dimension counterparts, a central theme of the series. In one future timeline, Ai grows up to become a respected soccer player, demonstrating the athletic prowess she shows even as a child, but this career ends in tragedy when she injures her foot so severely that it requires amputation. This leads her into a deep depression, and she nearly commits suicide by jumping from a hospital roof, only to be saved by Isami.

In another parallel dimension, that of the doomed future world of La'cryma, her counterpart is Lady Amamiku, a respected and powerful scientist. In this role, she is one of the key figures attempting to use Haruka and the Dragon Torque to save her reality from destruction, demonstrating her intelligence and determination in a vastly different context. The contrast between these versions of Ai highlights her potential for both athletic excellence and scientific achievement, as well as her vulnerability to despair when those potentials are broken. Throughout the present-day narrative, she is shown dealing with ordinary family events, such as her parents' wedding ceremony, which the fantastical elements of the plot frequently intrude upon. Her notable abilities include her expertise in soccer and her physical toughness, both of which are consistent traits across her various dimensional selves.