Kid is Kano's "little brother" personality. He is a vegan, and he says that he can "hear them [the animals] scream." He has shown magic powers when he is not in Kano's mind. Red does not know about him; Kano may or may not. He has a kid's sense of humor and claims to be various people when Mindi asks him who he is. When he is not out and about, Kid lives in Kano's head, sorting boxes with labels referring to Kano's thoughts and memories. He is chased by the "Breaking Noise" which he claims is Dark's shadow. When he is first introduced in book 1, he is used mainly as comic relief, balancing out Red's and Kano's darker aspects.
In later books, Kid plays the horror role of the scared innocent and spends most of his time in the Warehouse, sorting the boxes in Kano's mind. Some of these boxes contain monsters, but he claims that one holds his little sister who is protected by Orbkiller from going to hell.
Inside Kano's head, he looks like an eight year old child with short reddish blond hair and blue eyes. When he's "out" his appearance is only distinguished from regular Kano by his eye color (and, for readers, the color of the text in his dialogue.)
When Kid is first seen in Kano's mental landscape, he's wearing bright blue clothes, a purple kid's backback with a stuffed animal in it, and rainbow socks over his arms. After Dark leaves the Morgue and the Breaking Noise attacks him, his clothing switches to mirror Dark's own, with black clothes and bandages on his arms. He is later depicted with a blue hoodie, black shirt, two white band-aids in a cross, black sandals and dark blue shorts. 
Kid is very sensitive to the feelings of others, partly due to the fact that he seems to have ESP, and can hear the voices of animals. He loves animals (which is why he doesn't eat meat) and gets along famously with Djinnko and Djannko the fox twins. When he was staying with Cho in Nishi village, he staged protests against the local butcher, Kail, attempting to "liberate" his chickens, and called him "MERCHANT OF DEATH!"
Kid claims to have met Heyoka before Red was around, or at the very least, before Red made his presence amongst the Zones known.  However we see only a few pages later that Kano and Heyoka first meet after Red and Kano's fateful meeting at the gas station. This casts doubt of Kid's explanation unless Red was a lurking presence in Kano's head for awhile.