Hisui, sometimes called Harriet in other regions, is an elderly resident of Fula City. Fifty years before the film's events, she was caught in a mountain forest fire near the city. Her Snubbull gave its life to retrieve a key for the turbine at the wind power plant she had constructed. The incident left her with burns on her right hand, leading her to wear a prominent glove even in warm weather. This loss bred a deep-seated distrust and aversion to Pokémon.

Her general demeanor is grumpy and complaint-ridden, particularly when Pokémon are present—a behavior rooted in the guilt and pain of her past. An unintended exposure to a Sweet Scent compound caused Pokémon to be persistently drawn to her, worsening her distress and prompting her to seek a way to remove the scent.

Amid a later crisis involving Effect Spore and a new fire, she joined Pokémon to manually turn the turbine blades at the power plant, aiding in the dispersal of an antidote. This cooperation marked the beginning of a shift in her attitude, gradually softening her long-held resistance toward Pokémon.