The initial focus of the plot is Megumi entering her first year at Gale Medical, where she finds herself slightly ostracized by the fault of her own anxieties and social insecurities. She meets Kiden Rusen on her orientation day, and she slowly comes to accept his company. The story later focuses more Megumi's work alongside Kiden in the clinic, and then eventually on Megumi's own illness.
Megumi is extremely skeptical of her surroundings at any given time, and rarely admits to appreciating much in anything. She complains about almost everything, usually only to herself. She doesn't like to socialize with others, and takes note of all the bad qualities in people. She gets angry easily, and can be provoked by people bothering her too much. Megumi shows a different side to Haruko, and is quick to provide for her sister in any way. Only when Megumi is alone or with Haruko do certain anxieties and worries in Megumi's mind become apparent.
Megumi was raised entirely from infancy by Mary Nakahara, who is her official adoptive mother. Megumi is shown as having a very close relationship with Mary, and in most cases Mary is the adult Megumi is referencing when she refers to her mother. As Megumi gets older, she begins to distance herself from her family, Mary in particular. She even goes so far as to stop calling Mary 'Mom', referring to her by first name or 'Miss Nakahara' instead.
An important figure in Megumi's life, Haruko Nakahara is her adoptive older sister. While Haruko is in fact a year older than Megumi, Haruko often takes on the role of a more vulnerable and dependent sibling. Haruko is the only person that Megumi is shown fully opening up to and allowing into her new independent life. Haruko often visits Megumi's house and the two remain close even while Megumi attempts to distance herself from the dependency on her family.
Megumi's biological mother is absent from the series almost entirely, having died when Megumi was born. Although Megumi grew up with positive and loving impressions of her real mother through stories from Mary, she begins to harbor a growing resentment towards her birth parents as she approaches adolescence, to the point where using money left by her birth mother leaves her feeling bitter.
Megumi's biological father is also absent from the series, and not mentioned as often as her mother. Even in her adoptive family, both Megumi and Haruko lack a father figure.
Megumi enters her first year of schooling at Gale Medical at the start of A Doll's Medicine. Her tuition is paid for by money left behind by her mother, as well as money from Mary. Megumi is evidently using her new life at school to allow herself to feel independent, and takes pride in her spot at Gale. She still, however, is shown criticizing much of the architecture and faculty as well as fellow students.
Megumi discovers early in her first year at school that physical education is her favourite class, and she enjoys gym despite not forming very close relationships with the other girls in her group. Megumi excels at physical training and sports, and is frustrated by the lack of emphasis on such things at Gale Medical. Despite the overall defense-oriented training at Gale, Megumi picks up a lot of offensive and combat techniques through her own efforts in gym.
Megumi is also a relatively skilled painter, being able to use paint to recreate things she sees around her. It is noted by Kiden, however, that Megumi lacks creativity completely and can only paint things she looks at or has looked at in real life, unable to visualize anything new or come up with anything from her imagination.
Megumi can play the clarinet with accompanying sheet music, as she used to play songs with Haruko as children. However, Kiden notes a similar situation in Megumi's musical talents as with her painting ones, as Megumi has no interest in creating original compositions or playing anything but established songs with prescribed melodies.
An increasingly large focus in the plot is on Megumi's illness, which is only vaguely mentioned by those around her.