Aoi Tanio is a woman convicted of murder and the reason that Guardian Serpent of Tsukana Swamp requested the help of Kotoko Iwanaga in Chapter 15 of the Manga and Episode 2 of the Anime.

She is the main suspect of a murder for disposing a dead body into the Tsukuna Swamp. Furthermore, the serpent claims to have heard her utters: "I really hope they find it," after disposing the body.