Seol Kyung-hee is the older sister of Seol Kang-woo, and her body has been taken over by a parasite. In the early part of the story, she functions as a loyal member of the parasite organization led by the Pastor, serving as a formidable fighter and a recurring threat to the protagonists. As the series progresses, however, the parasite inhabiting her begins to exhibit more complex behaviors than its peers, partly due to lingering memories and biological remnants of the original Kyung-hee. This shift allows her character to explore the idea of a parasite developing a sense of individual identity or familial connection. Realizing that the Pastor’s plan treats other parasites as expendable, she chooses to break from the collective and forms an uneasy, temporary alliance with Kang-woo and Jeong Su-in. In the final conflict, she assists her brother and Su-in in an effort to stop the Pastor’s ascension, ultimately sacrificing herself. Her role in the story moves from that of a loyal soldier to a rogue element, and her development highlights the possibility of change even within a parasitic host. Notable abilities include the standard parasite capabilities: shapeshifting her head into weapon forms, enhanced physical strength, and combat proficiency. Her key relationships are defined by her biological bond with Kang-woo, her subordination to the Pastor, and her eventual cooperation with Su-in and the hybrid Heidi.