Kena Soga is a student at the Constant Magic Academy and serves as a central figure in the story. Her background is deeply intertwined with the world's fundamental mysteries. She shares her existence with a divine entity known as the Law of Identity, which is described as the true god of the universe and the principle that allows all beings to recognize themselves as individuals. While she and the Law of Identity share the same identity, their personalities, knowledge, and power are vastly different. This connection grants her an immortal nature, as she will reincarnate any number of times as long as the Law exists. Later in the narrative, after the death of Empress Kazuko, the Imperial Regalia chooses Kena as her successor, naming her the new Empress of Japan.

On the surface, Kena appears to be a ditzy and eccentric girl who is notably obsessed with rice, old fantasy books, and video games. She often acts in a carefree and seemingly oblivious manner, which can give the impression of her being annoying or simple-minded. However, this exterior is deceptive, as she is revealed to be a very smart student with outstanding grades in everything except practical magic. Her feelings are consistently shown to be true and sincere, and beneath her lighthearted demeanor lies a perceptive and deeply kind individual. Her primary motivation stems from her bond with the protagonist, Akuto Sai, whom she views as her prince. Her actions are largely driven by a desire to support and remain close to him, often acting as a calming and understated presence even in the face of danger.

Kena's role in the story is multifaceted and evolves significantly from a seemingly minor classmate into a figure of immense cosmic importance. Initially, she functions as a gentle and supportive friend to Akuto, one of the few who does not immediately judge him based on his prophesied future as the Demon King. As the narrative progresses, her true nature as the vessel for the Law of Identity comes to the forefront, making her the target of powerful individuals who seek to control or harness that divine power. She becomes the key to the world's underlying metaphysical structure and ultimately assumes the role of Empress, using the Imperial Regalia to command significant authority and power.

Regarding key relationships, her most significant connection is with Akuto Sai. The bond between them is ancient and profound, as they have a history that stretches back to childhood, symbolized by a bird-shaped hairpin that Akuto gave to a crying girl in the past, which Kena now wears. This connection only deepens as the series progresses, culminating in a metaphysical union where they perform the Contract of the One, casting aside their earthly forms to become a "Void Body" together. She also has a relationship with the entity known as the Law of Identity, of which she is the human vessel. While they share an identity, Kena acts as a distinct persona from the true god, who is far more omniscient and impersonal.

Throughout the story, Kena undergoes a dramatic transformation in her role and capabilities. She begins as an academically gifted but magically unremarkable student who hides her mana to go undetected and can turn invisible, although her clothes remain visible. Her development is not a change in personality but an awakening of her true nature. As her connection to the Law of Identity becomes more apparent and she accepts her position as Empress, she gains access to the Imperial Regalia, which grants her abilities such as creating powerful mana spheres, summoning swords of intense heat, and even suppressing the power of the Demon King. Her ultimate development is her transcendence of her human form, merging with Akuto Sai and the Law of Identity to exist beyond all stories as a Void Body, a state of existence that is empty and beyond normal conception.

Kena's notable abilities are vast and vary depending on her state of being. As a student, she possesses superhuman physical characteristics, the ability to fly, extrasensory perception to trace mana, and the power to manipulate a virtual alternate dimension, which allows her to change its rules or banish people into it. As Empress Keena, she can use the Imperial Regalia for energy projection, creation of multiple attacks simultaneously, and power nullification. In her ultimate form as the Law of Identity, her power is nearly boundless, including reality warping, plot manipulation, conceptual manipulation, existence erasure, and control over all stories, time, space, and causality. She perceives all of creation, even worlds with infinite dimensions, as mere fiction.