Kim Seong-a (Hangul: , also written as Kim Seong-ah in Mobile remake version and Kim Sung-a in some promotional material) is one of the main characters of White Day: A Labyrinth Named School. She was a student of Yeondu High School and was present during the events that took place on the night of March 13, 2001.

Another student trapped inside the building overnight, Kim Seong is a confident and outspoken girl who's jealous the attention So-Young Han receives. Quick to temper, she demands a lot.