Gleipnir (グレイプニル, Gureipuniru) is a Japanese manga series by Sun Takeda. It has been serialized in Kodansha's seinen manga magazine Young Magazine the 3rd since October 2015 and has been collected in eight tankōbon volumes. The manga is published in North America by Kodansha Comics. An anime television series adaptation by Pine Jam premiered on April 5, 2020.

The story centers on Shuichi Kagaya, a high school student with an unusual secret. He has the ability to transform into a monster resembling a giant dog mascot costume with a zipper down his back and a large cartoonish smile. After rescuing a strange girl, Claire Aoki, from a warehouse fire, they join each other to search for Clair's sister, who is assumed to be responsible for the death of their parents.
source: https://en.m.wikipedia.org/wiki/Gleipnir_(manga)