Megumi Shimizu is a sixteen-year-old girl who was born and raised in the rural village of Sotoba. She is a high school student who nurses a deep and passionate hatred for her hometown, which she sees as a stifling, boring place full of unsophisticated people who mock her for her fashion-conscious and city-oriented personality. Her greatest dream is to escape Sotoba to live a glamorous life in a big city, where she imagines she will be scouted for show business and spend her nights at clubs. The only things she cares about in the village are her unrequited crush, a transfer student from the city named Natsuno Yuuki, and a new, western-style mansion built on a hill.

In her human life, Megumi is self-centered and often looks down on the other villagers, including her childhood friend Kaori Tanaka, whom she finds annoying. She acts polite on the surface but feels superior to those who are content with the simple village life. Her feelings for Natsuno are intense but unreciprocated, leading her to develop a habit of secretly watching him from outside his window and daydreaming about a relationship with him. She believes that because Natsuno is also from a city, he must share her desire to leave Sotoba, making them kindred spirits.

Megumi's life takes a tragic turn when she goes to visit the new mansion out of curiosity. She is killed by Chizuru Kirishiki, a member of the vampire family that has moved in. After her death, she becomes one of the first villagers to rise again as a Shiki, a reanimated corpse that survives on human blood. Her transformation strips away her human inhibitions, amplifying her negative traits into something far more malicious and sociopathic. As a Shiki, she embraces her new existence with little remorse, viewing the other villagers as prey and using her powers to terrorize them as revenge for their past mockery.

Her obsession with Natsuno evolves into a possessive and dangerous fixation. She kills his best friend, Tooru Mutou, out of jealousy over the attention Natsuno gives him. She also kills Kaori's father, both as an act of revenge against her former friend for getting close to Natsuno and on the orders of the Shiki leadership. Megumi shows no sympathy for her victims and seems to take pleasure in the suffering of the villagers she despises. Despite her cruelty towards almost everyone, her feelings for Natsuno are genuine, and she disobeys orders in an attempt to save him, showing that he remains her only true concern.

As a Shiki, Megumi gains several supernatural abilities common to her kind. She becomes immortal and can heal from wounds at a superhuman speed. She possesses enhanced physical strength and can see clearly in total darkness. She also gains the ability to hypnotize humans by biting them, allowing her to control their actions or plant suggestions. Like all Shiki, she can levitate for short periods and uses retractable fangs to drain blood from her victims, a process that also infects them with the venom that will cause them to rise as Shiki after death. Her appearance changes as well, with her skin becoming extremely pale and her eyes transforming to have black sclera and glowing crimson irises. She also becomes vulnerable to sunlight, which will burn her to death, and she cannot enter a home without first being invited. Despite her power, Megumi meets her end when the villagers of Sotoba finally rise up against the Shiki, hunting her down and destroying her with a stake through the heart.