Megumi Takani is a character who first appears in the Tokyo arc of the story as a young woman in a difficult situation. She is the youngest daughter of the Takani family, a renowned clan of physicians from the Aizu province who were known for their progressive belief in training women and children in medicine and treating all patients equally regardless of social status. The Takani family even went so far as to leave their clan to study Western medicine in Nagasaki, a serious act of defection at the time. This background instilled in Megumi a deep knowledge of both traditional Japanese practices, like moxibustion, and more modern Western techniques, particularly toxicology. Her life was shattered by the Boshin War, in which her father was killed and her mother and brothers went missing, leaving her the sole survivor of her family.

In the aftermath of this personal tragedy, Megumi eventually found herself in Tokyo working as an assistant to a doctor. This physician, however, was secretly collaborating with the corrupt industrialist Takeda Kanryu to manufacture a cheap and highly addictive form of opium. When the doctor was killed for demanding a larger share of the profits, Megumi was forcibly held captive and compelled to use her medical expertise to produce the drug for Kanryu. This experience left her with immense guilt and self-loathing, as she felt responsible for the lives destroyed by the drug she was forced to create. Desperate to escape, she fled from Kanryu's compound and literally ran into the wandering swordsman Himura Kenshin and his friend Sagara Sanosuke, seeking their protection.

In her initial interactions, Megumi can appear guarded and manipulative, flirting with Kenshin as a means to secure her own safety and initially planning to abandon her rescuers if the situation became too dangerous. Sanosuke and Kaoru Kamiya, the master of the dojo where she finds shelter, nickname her a "vixen" due to her playful yet sharp-tongued demeanor and her tendency to tease others, especially Kaoru. However, this flirtatious and somewhat prickly exterior conceals a profoundly guilt-ridden and serious interior. After Kenshin and his allies defeat Kanryu and his private army of former shinobi, the Oniwabanshu, Megumi is so overcome with remorse for her past actions that she attempts to kill herself. She is stopped by Sanosuke and Kenshin, who inspires her to atone not by dying, but by living and using her skills to save as many people as she possibly can.

This moment defines her role in the story going forward. Choosing to follow Kenshin's advice, she becomes the primary physician for the main characters and the local community. She apprentices under the kind doctor Oguni Gensai, taking over most of the medical duties and tending to the wounds of the group after their many battles, particularly for the often-injured Sanosuke. Her motivations shift from self-preservation to redemption through service. She is deeply dedicated to healing others, a commitment so strong that she continues to treat opium addicts for free, seeing it as part of her penance.

Megumi develops a complex and unrequited romantic love for Kenshin, who was the catalyst for her transformation. She often playfully flirts with him, much to the jealousy of Kaoru, who is Kenshin's love interest. However, Megumi is emotionally intelligent and perceptive; she fully recognizes the deep bond between Kenshin and Kaoru and ultimately steps aside, never seriously pursuing him and instead becoming a quiet, mature supporter of their relationship. She forms a unique friendship with Kaoru, acting as a teasing older sister figure who can have honest, "female-to-female" conversations with her about matters of the heart. Her relationship with Sanosuke is notably different, marked by a constant, good-natured bickering and mutual teasing that, over time, suggests a comfortable and deepening closeness.

Beyond her interpersonal relationships, Megumi's medical abilities are her most notable asset. She is highly skilled in diagnosing and treating a wide range of ailments, from broken bones and lacerations to complex poisonings. She is the first to notice subtle but dangerous physical changes in Kenshin's body, demonstrating her keen observational skills and advanced knowledge of physiology. She is also an excellent cook, a talent that even the often-grumpy young Yahiko Myojin appreciates. After the main conflict of the story concludes, she fulfills her earlier desire to return to her homeland, going back to Aizu to set up a clinic and serve the community where there is a shortage of doctors, thus completing her journey from a victim forced to destroy lives to a healer dedicated to saving them.