At first, Hiroko is a seemingly kind innocent young child, though later, after numerous (childish) traps and tricks were discovered in the house, Hime began suspecting her. Eventually, Hiroko was caught red-handed when preparing another trap, revealing her to be an assassin sent to kill Hime, though Hiro sensed that Hiroko was being controlled and did not mean to hurt anyone. Despite being forgiven by everyone, Hiroko ran away in shame, much to Hiro and Sawawa's sadness.
Later on, when Hime, Hiro, Riza and Reiri becomes trapped in their dreams, Hiroko is seen briefly by Hiro before disappearing into the darkness.
Hiroko is very weak compared to other characters, even Hiro. As a result she tends to use cheap tricks and booby traps to kill Hime, but because they were "made by a child", they are extremely simple and easy to avoid. She also has the power to turn herself into a cat and a little cat-girl if need be.