On an alternate Earth, the military is attacked and loses a monster-like creature during the battle. Later the monster is accidentally found by 2 young boys, and they decide to make him their pet. Grumble (the monster) grows up with the boys, and they make a few more friends along the way. They soon realize that he's no longer a pet, but an amazing friend. This is a story about Grumble's journey through life, as he tries to figure out what he is, where he belongs…and his true destiny. <https://www.facebook.com/grumblemanga>