Sannokuchi is a small yōkai serving the Nura Clan, named for his distinctive mouth shaped like the number "3," which serves as his primary identifier. He possesses grey eyes and no hair. He consistently appears alongside three specific companions: Nattō Kozō, Tōfu Kozō, and Ko-oni. This group often engages in communal activities like playing the board game Go or organizing small banquets together. Sannokuchi boasts a long presence within the Nura Clan, having participated in both Nurarihyon's and Rihan's Hyakki Yakō (Night Parade of One Hundred Demons). Before joining the Nura Clan, Sannokuchi existed as a Mayoi-Ga in Toono. In this role, he employed fear-based illusions to mislead and disorient human guests entering houses; these manifestations dissipated when his fear-inducing abilities ceased. Sannokuchi notably appeared as the sole non-main cast character in the Jump Festa special presentation. He also achieved 32nd place in the series' first character popularity poll, receiving 87 votes.