A friend of Erika Karisawa and a member of the Dollars gang.
Walker is a cheerful boy and a big anime/manga otaku, but that smile hides a darker, sadistic side. With his friend Erika, he is not averse to torturing people when the situation calls for it or when he feels the need to make a point. For example, when his group successfully tracked down some kidnappers, he threw down a stack of serial manga magazines and offered to let the victim pick the theme of his own torture based on the manga displayed on the cover. The man picked Kuroshitsuji, so Walker and Erika threatened to poke his eye out with an icepick until he broke and told them what he knew.
Apparently he was a former member of the Blue Squares with Kyohei, Erika and Saburo, but grew disgusted with them after they tortured Saki to the point where he torched a van containing Blue Square members with a molotov cocktail to rescue her.
Walker is always shown to have his eyes closed, but when he opens them, it's usually a bad sign.