Makiko Gregory is a reserved and elusive half-British, half-Japanese university student. Her quiet, detached exterior often projects an air of innocence. Beneath this facade, she engages in psychological manipulation, particularly within her codependent relationship with her boyfriend, Yesterday Taguchi. Their dynamic is mutually dysfunctional: Makiko cultivates Yesterday's reliance on her while simultaneously craving his control over her, creating a cycle that prevents resolution. She rarely communicates her true feelings or intentions clearly. As part of her manipulation, she occasionally feigns an inability to speak Japanese, pretending to understand only English.

She participates in the Abnormal Physiology Seminar's unconventional experiments, her impassive reactions masking her true feelings about these activities. Makiko claims to experience dissociative episodes, becoming lost in thought and unaware of her surroundings, and reports gaps in her memory regarding her personal history. Whether these memory lapses are genuine or a psychological defense mechanism remains unclear.

Academically diligent and serving as Yesterday's assistant, she earns respect from peers and instructors despite her idiosyncrasies. Makiko exhibits perfectionist tendencies in her work and harbors an obsession with bodily fluids and waste products, including consuming her own urine. This behavior leads to ridicule and bullying from classmates, yet she refuses to conform. Her mixed heritage remains a stated trait.

Her relationship with Yesterday persists in stagnation, both perpetuating their dysfunctional interdependence. Though she occasionally signals a desire for normalization, she undermines progress through inconsistent communication and persistent psychological games. Her reactions to the seminar's explicit or taboo activities are consistently neutral, leaving her personal stance obscure.