One of three people living inside Guu's stomach world who first appears in episode 8 of the TV series. She is a 22 year old who attempted suicide by throwing herself into the ocean and was rescued by Guu, who swallowed her while fishing (and while bringing in a massive haul of various sea life, she technically didn't catch any fish). Unlike Seiichi and Tomoyo, Hiroko is mentally unstable and Bipolar, making her dangerous and unpredictable. In fact, she tried to kill herself in an elaborate plot to take revenge on her cheating husband by dying, going through hell, and coming back as an evil spirit to haunt him for the rest of his life. She now spends most of her time in Guu's stomach world drinking alone on a hill, where most of the other inhabitants have now learned to avoid. Became fast-friends with Yumi-sensei when Guu had swallowed Yumi for a short time.