Kaf Morisaki is the central protagonist of the Kamitsubaki City Under Construction narrative, a first-year high school student whose life is defined by a deep, unwavering love for singing. Before the events of the story, she was an ordinary girl with average grades and little aptitude for sports, but her world was shattered by a catastrophic disaster known as the Blackout, a mysterious event where a green light incinerated those it touched. Kaf survived this event, a survival she later learns was due to her inherent connection to song, but she suffered the immense trauma of finding the bodies of her parents, who were not so fortunate. Orphaned, she was taken in by a kind neighbor named Erika.

In terms of personality, Kaf is naturally cheerful and energetic. However, her sense of motivation is not rooted in a grand or idealistic sense of justice, such as a vow to never forgive evil. Instead, she is driven by a personal and visceral compass, instinctively standing up against anything she personally finds to be unreasonable, unfair, or illogical. This direct, instinct-driven nature allows her to form close bonds with those around her, who are often drawn to her positive energy. Her core motivation is intrinsically linked to her voice, as singing is not just her favorite pastime but becomes her unique power and purpose. Seven years after the Blackout, Kaf is a teenager living in a city still rebuilding and now plagued by new supernatural phenomena called Q, which create monsters known as tesseractors. Her casual singing attracts the attention of a mysterious young boy named Laplace, who reveals that she is a witchling, a person with the ability to destroy these monsters through the power of her songs, essentially purifying the trapped human souls within them. This revelation is brutally underscored when she witnesses her guardian, Erika, killed by a tesseractor, solidifying her tragic role in the city's defense.

Kaf’s role in the story is that of a witchling, a special being tasked with protecting Kamitsubaki City from the tesseractors and the Incomprehensible Regions they create, which are side effects of the city's energy source. She is partnered with Laplace, who transforms from a fish-like form to support her in combat, specifically in targeting aerial threats. Her key relationships are forged with her fellow witchlings, who are also students and protectors of the city: the almost perfect heiress Rime Tanioki, who becomes her roommate; the free-spirited Haru Asanushi; the naive yet strong-willed Sekai Yorukawa; and the compassionate Koko Rinne. Her relationship with the city’s Reconstruction Division Chief is complex, as the Chief initially regards the witchlings as necessary sacrifices for the city's survival, a cold logic that Kaf challenges in her wish to understand and value human life more deeply. Her development is a harrowing journey of trauma and resilience. After discovering the repeated, cyclical nature of the city's destruction, where a failsafe called Phenomenon resets the timeline after humanity is wiped out, Kaf’s spirit is crushed. Overwhelmed by the fear that her songs could overwrite human emotions or that her reality is a fabricated simulation, she falls into a state of deep despair, losing her ability or will to sing and even temporarily transforming into the very tesseractors she once fought.

Kaf’s most notable ability is her singing voice, which she loves more than anything else. As a witchling, her songs possess the supernatural power to purify tesseractors, freeing the anguished human spirit trapped within the monster and dispelling the negative emotions that created it. At higher stakes, the collective songs of the witchlings have the potential to be even more powerful, capable of rewriting the rules of reality itself, a power that both defines her purpose and becomes the source of her deepest fear.