Ki-Seok is a supporting character in the South Korean Netflix series Parasyte: The Grey, portrayed by actor Yoo Yong. His primary role in the narrative is defined by his close friendship with the main character,薛强祐 Seol Kang-woo, to whom he is identified as a best friend.

In terms of personality, Ki-Seok is presented as a fundamentally kind and sweet individual. His nature is such that his ultimate action, a significant self-sacrifice, is described as being entirely in character and thus a shocking but believable turn for the audience. This act of sacrifice is the most notable event tied to his character, leaving a strong emotional impact.

The character also undergoes a dramatic transformation that showcases the central horror premise of the series. Ki-Seok is one of the humans who becomes a host to a parasitic life form. The performance requires a stark and impressive switch from portraying a nice, emotive human to becoming completely emotionless once the parasite takes control, highlighting the creature's inhuman nature. No further specific details are available regarding his background, other key relationships, motivations, or any unique abilities.