Kyoko Machi is a dullahan, a rare demi-human whose head remains permanently detached from her body. A blue or green flame flickers from her neck, the point where her head should connect. Because her head cannot move independently, she must carry it constantly. This condition manifested unexpectedly during her toddler years; she was born appearing fully human.

Physically, Kyoko possesses fair skin, spiky ginger hair kept short for practicality, and blue eyes. Her frame is taller and more developed than many peers, with arms notably muscular from perpetually holding her head. She wears standard school uniforms but requires a sweatervest in summer to prevent visibility issues caused by perspiration. Carrying her head often leads to accidental bumps against her chest while walking.

Patient, kind, and intellectually curious, Kyoko developed methods to perform tasks requiring both hands despite her constant burden. Academically gifted, she ranked fifth in midterms and first in proficiency exams. She enjoys studying and assisting friends but flusters easily. Isolation distresses her due to reliance on others for mobility, and she strongly craves physical affection like hugs or having her head held.

Initial social interactions proved challenging. Classmates avoided mentioning her detached head despite her acceptance of it, creating awkwardness. This improved after biology teacher Tetsuo Takahashi advised her on guiding conversations about her condition, helping peers understand comfortable interaction. He also facilitated school permission for her to use a backpack, easing daily logistics.

Her relationships include a close friendship with Hikari Takanashi (though she disapproves of Hikari's mischievous handling of her body), mutual understanding with Yuki Kusakabe after resolving early distancing caused by Yuki's fear of harming others, and camaraderie with Sakie Sato, sharing discussions about romantic interests. Kyoko harbors a schoolgirl crush on Takahashi, appreciating his support, though physical contact sometimes causes mutual awkwardness due to unintended proximity.

Medical scans confirmed her neck structure exists in "another space," functioning as a biological wormhole connecting her head to her body internally. Kyoko aspires to research dullahan physiology ethically, believing her firsthand experience could unlock scientific understanding. Only two other dullahans are known globally.

Her development shows progression from shyness to proactive social integration. An experimental "date" with Takahashi highlighted practical challenges like motion sickness from unstable head carrying but reinforced her comfort with him. She gradually expresses emotions more freely, with her neck flame flaring noticeably during intense reactions. Her journey emphasizes adaptation to physical differences and pursuit of self-acceptance through academic goals and interpersonal connections.