Mopoko is Hiaté's first Created, an odd balloon creature who can change his size by inhaling or exhaling large quantities of air. His abilities revolve mainly around the creative use of this skill, such as exhaling rapidly to make himself into a manner of missile to attack his foes. The fact he can find such uses for his abilities is a sign of the creature's intelligence, something that is typically underestimated thanks to his cute appearance and small stature.
He seems to have some small amount of telepathic skill, which he uses to communicate with Hiaté, who he calls "Mama." This seems to be his only means of communication, as verbally he only seems capable of stating fragments of his own name. He is very loyal and obedient to his Summoner, and is also very protective of her. When he's large enough, he'll even let her ride round on his back as a mode of transportation.