"Gleipnir" is a Japanese manga series written and illustrated by Sun Takeda. The story follows a high school student named Shuichi Kagaya who can transform into a giant monster with a zipper on his back. One day, he meets a girl named Claire Aoki who knows his secret and forces him to help her find her missing sister. As they search for clues, they become involved in a dangerous game where they must battle other monsters who also possess unique abilities. The series explores themes of identity, power, and the consequences of one's actions.