Yamawaro

A hell creature commanded by the new Hell Girl in season 3, who takes on the look of a young boy, though he can also become a yellow/green straw doll. In human form, he calls himself by the name of Huang (黄). Often quiet and having a gentle demeanor, not much is known about him. He follows Kikuri on their assignments in the real world, refering to her as "Hime". His name is derived from the same name given to a legendary mountain-dwelling creature in Kyūshū from Gazu Hyakki Yakō, an illustrated book on Japanese folklore demons. In Jigoku Shoujo Mitsuganae, he was used as an experiment for this doctor that tried to make a medicine to make people young again. Then he was filled with a fungus. from Wikipedia