Mio is Garu's beloved black cat and helper. He is often seen with his master, usually on his head or helping in his training/meditation. He is in love with Yani, Pucca's cat and is a rival to the Cat Clan. Yani returns Mio's affection, for example, in "Cat Napped", she shared her milk with him and cuddles with him in some episodes. He hates going to the vet because he is afraid of getting shots. Like Garu, Mio can split himself into clones with his "Miosion Illusion".
Like Garu, Mio knows ninja abilities but does them in a feline way. He sometimes appears to be training with Garu.