Gleipnir follows a high school student named Shuichi Kagaya who can transform into a monstrous, furry creature resembling a living costume, complete with a giant zipper on his back. His secret is discovered by a mysterious and troubled girl named Claire, who forces him into a partnership. Together, they search for other individuals with similar monstrous abilities and the coins that grant them power, hoping to uncover the truth behind their transformations and Claire's past. Readers enjoy the series for its dark, gritty take on body horror and supernatural battles, the tense and morally complex relationship between Shuichi and Claire, and the compelling mystery that slowly reveals a larger, more sinister game involving power, survival, and identity.